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Re: [PATCH] I2C: SiByte: Convert the driver to make use of interrupts

To: Matt Turner <mattst88@gmail.com>
Subject: Re: [PATCH] I2C: SiByte: Convert the driver to make use of interrupts
From: Jean Delvare <khali@linux-fr.org>
Date: Sat, 3 Sep 2011 10:30:36 +0200
Cc: linux-i2c@vger.kernel.org, linux-mips@linux-mips.org, Ralf Baechle <ralf@linux-mips.org>, Guenter Roeck <guenter.roeck@ericsson.com>, "Maciej W. Rozycki" <macro@linux-mips.org>
In-reply-to: <1313710991-3596-1-git-send-email-mattst88@gmail.com>
References: <1313710991-3596-1-git-send-email-mattst88@gmail.com>
Sender: linux-mips-bounce@linux-mips.org
Hi Matt,

On Thu, 18 Aug 2011 19:43:11 -0400, Matt Turner wrote:
> From: Maciej W. Rozycki <macro@linux-mips.org>
> 
> This is a rewrite of large parts of the driver mainly so that it uses
> SMBus interrupts to offload the CPU from busy-waiting on status inputs.
> As a part of the overhaul of the init and exit calls, all accesses to the
> hardware got converted to use accessory functions via an ioremap() cookie.

This could have been split into incremental patches, to make review
easier.

> [mattst88] Added BCM1480 interrupts and rebased minimally.

Ditto.

checkpatch complains about this, please fix:

WARNING: line over 80 characters
#257: FILE: drivers/i2c/busses/i2c-sibyte.c:157:
+       if (adap->status > 0 && ((adap->status & (M_SMB_ERROR | 
M_SMB_ERROR_TYPE)) == M_SMB_ERROR)) {

Very nice patch overall, I only have minor comments, see below inline.

> 
> Signed-off-by: Matt Turner <mattst88@gmail.com>
> Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
> ---
> This is the second version of this patch that I've sent. This version
> fixes the problem with the ENXIO return.
> 
>  drivers/i2c/busses/i2c-sibyte.c |  296 +++++++++++++++++++++++++++++---------
>  1 files changed, 226 insertions(+), 70 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-sibyte.c b/drivers/i2c/busses/i2c-sibyte.c
> index 0fe505d..d2f1cf1 100644
> --- a/drivers/i2c/busses/i2c-sibyte.c
> +++ b/drivers/i2c/busses/i2c-sibyte.c
> @@ -2,6 +2,7 @@
>   * Copyright (C) 2004 Steven J. Hill
>   * Copyright (C) 2001,2002,2003 Broadcom Corporation
>   * Copyright (C) 1995-2000 Simon G. Vogl
> + * Copyright (C) 2008 Maciej W. Rozycki

Wow, looks like this patch has been sleeping for quite some time...

>   *
>   * This program is free software; you can redistribute it and/or
>   * modify it under the terms of the GNU General Public License
> @@ -18,104 +19,164 @@
>   * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, 
> USA.
>   */
>  
> +#include <linux/errno.h>
> +#include <linux/interrupt.h>
>  #include <linux/kernel.h>
>  #include <linux/module.h>
>  #include <linux/init.h>
>  #include <linux/i2c.h>
> +#include <linux/param.h>
> +#include <linux/spinlock.h>
> +#include <linux/types.h>
> +#include <linux/wait.h>
>  #include <linux/io.h>
> +#include <asm/sibyte/sb1250_int.h>
>  #include <asm/sibyte/sb1250_regs.h>
>  #include <asm/sibyte/sb1250_smbus.h>
> +#include <asm/sibyte/bcm1480_int.h>
>  
>  
>  struct i2c_algo_sibyte_data {
> -     void *data;             /* private data */
> -     int   bus;              /* which bus */
> -     void *reg_base;         /* CSR base */
> +     wait_queue_head_t       wait;           /* IRQ queue */
> +     void __iomem            *csr;           /* mapped CSR handle */
> +     phys_t                  base;           /* physical CSR base */
> +     char                    *name;          /* IRQ handler name */

Should be a const pointer. Also, if the name is only for the IRQ, then
irq_name would be a better name.

> +     spinlock_t              lock;           /* atomiser */

A more useful comment would explain what exactly is being protected by
the lock.

> +     int                     irq;            /* IRQ line */
> +     int                     status;         /* IRQ status */

You could document than -1 means error.

>  };
>  
> -/* ----- global defines ----------------------------------------------- */
> -#define SMB_CSR(a,r) ((long)(a->reg_base + r))
>  
> +static irqreturn_t i2c_sibyte_interrupt(int irq, void *dev_id)
> +{
> +     struct i2c_adapter *i2c_adap = dev_id;
> +     struct i2c_algo_sibyte_data *adap = i2c_adap->algo_data;
> +     void __iomem *csr = adap->csr;
> +     u8 status;
> +
> +     /*
> +      * Ugh, no way to detect the finish interrupt,
> +      * but if busy it is obviously not one.
> +      */
> +     status = __raw_readq(csr + R_SMB_STATUS);
> +     if ((status & (M_SMB_ERROR | M_SMB_BUSY)) == M_SMB_BUSY)
> +             return IRQ_NONE;
> +
> +     /*
> +      * Clear the error interrupt (write 1 to clear);
> +      * the finish interrupt was cleared by the read above.
> +      */
> +     __raw_writeq(status, csr + R_SMB_STATUS);
> +
> +     /* Post the status. */
> +     spin_lock(&adap->lock);
> +     adap->status = status & (M_SMB_ERROR_TYPE | M_SMB_ERROR | M_SMB_BUSY);
> +     wake_up(&adap->wait);
> +     spin_unlock(&adap->lock);
> +
> +     return IRQ_HANDLED;
> +}
>  
> -static int smbus_xfer(struct i2c_adapter *i2c_adap, u16 addr,
> -                   unsigned short flags, char read_write,
> -                   u8 command, int size, union i2c_smbus_data * data)
> +static s32 i2c_sibyte_smbus_xfer(struct i2c_adapter *i2c_adap, u16 addr,
> +                              unsigned short cflags,
> +                              char read_write, u8 command, int size,
> +                              union i2c_smbus_data *data)
>  {
>       struct i2c_algo_sibyte_data *adap = i2c_adap->algo_data;
> +     void __iomem *csr = adap->csr;
> +     unsigned long flags;
>       int data_bytes = 0;
>       int error;
>  
> -     while (csr_in32(SMB_CSR(adap, R_SMB_STATUS)) & M_SMB_BUSY)
> -             ;
> +     spin_lock_irqsave(&adap->lock, flags);
> +
> +     if (adap->status < 0) {
> +             error = -EIO;
> +             goto out_unlock;
> +     }

Well, this can only happen if the previous transaction ended up with a
failure, right? This means that a single error will break the SMBus
forever. Is there no way to reset the controller to a sane state if
this happens?

>  
>       switch (size) {
>       case I2C_SMBUS_QUICK:
> -             csr_out32((V_SMB_ADDR(addr) |
> -                        (read_write == I2C_SMBUS_READ ? M_SMB_QDATA : 0) |
> -                        V_SMB_TT_QUICKCMD), SMB_CSR(adap, R_SMB_START));
> +             __raw_writeq(V_SMB_ADDR(addr) |
> +                          (read_write == I2C_SMBUS_READ ? M_SMB_QDATA : 0) |
> +                          V_SMB_TT_QUICKCMD,
> +                          csr + R_SMB_START);
>               break;
>       case I2C_SMBUS_BYTE:
>               if (read_write == I2C_SMBUS_READ) {
> -                     csr_out32((V_SMB_ADDR(addr) | V_SMB_TT_RD1BYTE),
> -                               SMB_CSR(adap, R_SMB_START));
> +                     __raw_writeq(V_SMB_ADDR(addr) | V_SMB_TT_RD1BYTE,
> +                                  csr + R_SMB_START);
>                       data_bytes = 1;
>               } else {
> -                     csr_out32(V_SMB_CMD(command), SMB_CSR(adap, R_SMB_CMD));
> -                     csr_out32((V_SMB_ADDR(addr) | V_SMB_TT_WR1BYTE),
> -                               SMB_CSR(adap, R_SMB_START));
> +                     __raw_writeq(V_SMB_CMD(command), csr + R_SMB_CMD);
> +                     __raw_writeq(V_SMB_ADDR(addr) | V_SMB_TT_WR1BYTE,
> +                                  csr + R_SMB_START);
>               }
>               break;
>       case I2C_SMBUS_BYTE_DATA:
> -             csr_out32(V_SMB_CMD(command), SMB_CSR(adap, R_SMB_CMD));
> +             __raw_writeq(V_SMB_CMD(command), csr + R_SMB_CMD);
>               if (read_write == I2C_SMBUS_READ) {
> -                     csr_out32((V_SMB_ADDR(addr) | V_SMB_TT_CMD_RD1BYTE),
> -                               SMB_CSR(adap, R_SMB_START));
> +                     __raw_writeq(V_SMB_ADDR(addr) | V_SMB_TT_CMD_RD1BYTE,
> +                                  csr + R_SMB_START);
>                       data_bytes = 1;
>               } else {
> -                     csr_out32(V_SMB_LB(data->byte),
> -                               SMB_CSR(adap, R_SMB_DATA));
> -                     csr_out32((V_SMB_ADDR(addr) | V_SMB_TT_WR2BYTE),
> -                               SMB_CSR(adap, R_SMB_START));
> +                     __raw_writeq(V_SMB_LB(data->byte), csr + R_SMB_DATA);
> +                     __raw_writeq(V_SMB_ADDR(addr) | V_SMB_TT_WR2BYTE,
> +                                  csr + R_SMB_START);
>               }
>               break;
>       case I2C_SMBUS_WORD_DATA:
> -             csr_out32(V_SMB_CMD(command), SMB_CSR(adap, R_SMB_CMD));
> +             __raw_writeq(V_SMB_CMD(command), csr + R_SMB_CMD);
>               if (read_write == I2C_SMBUS_READ) {
> -                     csr_out32((V_SMB_ADDR(addr) | V_SMB_TT_CMD_RD2BYTE),
> -                               SMB_CSR(adap, R_SMB_START));
> +                     __raw_writeq(V_SMB_ADDR(addr) | V_SMB_TT_CMD_RD2BYTE,
> +                                  csr + R_SMB_START);
>                       data_bytes = 2;
>               } else {
> -                     csr_out32(V_SMB_LB(data->word & 0xff),
> -                               SMB_CSR(adap, R_SMB_DATA));
> -                     csr_out32(V_SMB_MB(data->word >> 8),
> -                               SMB_CSR(adap, R_SMB_DATA));
> -                     csr_out32((V_SMB_ADDR(addr) | V_SMB_TT_WR2BYTE),
> -                               SMB_CSR(adap, R_SMB_START));
> +                     __raw_writeq(V_SMB_LB(data->word & 0xff),
> +                                  csr + R_SMB_DATA);
> +                     __raw_writeq(V_SMB_MB(data->word >> 8),
> +                                  csr + R_SMB_DATA);
> +                     __raw_writeq(V_SMB_ADDR(addr) | V_SMB_TT_WR2BYTE,
> +                                  csr + R_SMB_START);
>               }
>               break;
>       default:
> -             return -EOPNOTSUPP;
> +             error = -EOPNOTSUPP;
> +             goto out_unlock;
>       }
> +     mmiowb();
> +     __raw_readq(csr + R_SMB_START);
> +     adap->status = -1;
> +
> +     spin_unlock_irqrestore(&adap->lock, flags);
>  
> -     while (csr_in32(SMB_CSR(adap, R_SMB_STATUS)) & M_SMB_BUSY)
> -             ;
> +     wait_event_timeout(adap->wait, (adap->status >= 0), HZ);

1 second is a rather long timeout. The driver only supports small
transactions, so even if a slave slows down the clock, I can hardly
imagine a transaction lasting more that, say, 10 ms. So I think you can
safely lower the timeout to HZ / 5 or even HZ / 10.

Also, shouldn't you check the return value? This would let you return
the right error code (-ETIMEDOUT according to
Documentation/i2c/fault-codes) and you would no longer have to check
for adap->status sign in the rest of the function.

>  
> -     error = csr_in32(SMB_CSR(adap, R_SMB_STATUS));
> -     if (error & M_SMB_ERROR) {
> -             /* Clear error bit by writing a 1 */
> -             csr_out32(M_SMB_ERROR, SMB_CSR(adap, R_SMB_STATUS));
> -             return (error & M_SMB_ERROR_TYPE) ? -EIO : -ENXIO;
> +     spin_lock_irqsave(&adap->lock, flags);
> +
> +     if (adap->status > 0 && ((adap->status & (M_SMB_ERROR | 
> M_SMB_ERROR_TYPE)) == M_SMB_ERROR)) {
> +             error = -ENXIO;
> +             goto out_unlock;
> +     }
> +     if (adap->status < 0 || (adap->status & (M_SMB_ERROR | M_SMB_BUSY))) {
> +             error = -EIO;
> +             goto out_unlock;
>       }
>  
>       if (data_bytes == 1)
> -             data->byte = csr_in32(SMB_CSR(adap, R_SMB_DATA)) & 0xff;
> +             data->byte = __raw_readq(csr + R_SMB_DATA) & 0xff;
>       if (data_bytes == 2)
> -             data->word = csr_in32(SMB_CSR(adap, R_SMB_DATA)) & 0xffff;
> +             data->word = __raw_readq(csr + R_SMB_DATA) & 0xffff;
>  
> -     return 0;
> +     error = 0;
> +
> +out_unlock:
> +     spin_unlock_irqrestore(&adap->lock, flags);
> +
> +     return error;
>  }
>  
> -static u32 bit_func(struct i2c_adapter *adap)
> +static u32 i2c_sibyte_bit_func(struct i2c_adapter *adap)

If you're renaming this then please drop the "bit" part in it, it's
most likely coming from a copy-and-paste from i2c-algo-bit and has no
meaning in the sibyte driver.

>  {
>       return (I2C_FUNC_SMBUS_QUICK | I2C_FUNC_SMBUS_BYTE |
>               I2C_FUNC_SMBUS_BYTE_DATA | I2C_FUNC_SMBUS_WORD_DATA);
> @@ -125,8 +186,8 @@ static u32 bit_func(struct i2c_adapter *adap)
>  /* -----exported algorithm data: -------------------------------------       
> */
>  
>  static const struct i2c_algorithm i2c_sibyte_algo = {
> -     .smbus_xfer     = smbus_xfer,
> -     .functionality  = bit_func,
> +     .smbus_xfer     = i2c_sibyte_smbus_xfer,
> +     .functionality  = i2c_sibyte_bit_func,
>  };
>  
>  /*
> @@ -135,37 +196,121 @@ static const struct i2c_algorithm i2c_sibyte_algo = {
>  static int __init i2c_sibyte_add_bus(struct i2c_adapter *i2c_adap, int speed)
>  {
>       struct i2c_algo_sibyte_data *adap = i2c_adap->algo_data;
> +     void __iomem *csr;
> +     int err;
>  
> -     /* Register new adapter to i2c module... */
> -     i2c_adap->algo = &i2c_sibyte_algo;
> +     adap->status = 0;
> +     init_waitqueue_head(&adap->wait);
> +     spin_lock_init(&adap->lock);
> +
> +     csr = ioremap(adap->base, R_SMB_PEC + SMB_REGISTER_SPACING);
> +     if (!csr) {
> +             err = -ENOMEM;
> +             goto out;
> +     }
> +     adap->csr = csr;
>  
>       /* Set the requested frequency. */
> -     csr_out32(speed, SMB_CSR(adap,R_SMB_FREQ));
> -     csr_out32(0, SMB_CSR(adap,R_SMB_CONTROL));
> +     __raw_writeq(speed, csr + R_SMB_FREQ);
> +
> +     /* Clear any pending error interrupt. */
> +     __raw_writeq(__raw_readq(csr + R_SMB_STATUS), csr + R_SMB_STATUS);
> +     /* Disable interrupts. */
> +     __raw_writeq(0, csr + R_SMB_CONTROL);
> +     mmiowb();
> +     __raw_readq(csr + R_SMB_CONTROL);

Shouldn't it be the other way around, disable interrupts first and then
clear any pending one? Looks racy otherwise, but maybe it makes no
difference in practice.

> +
> +     err = request_irq(adap->irq, i2c_sibyte_interrupt, IRQF_SHARED,
> +                       adap->name, i2c_adap);
> +     if (err < 0)
> +             goto out_unmap;
> +
> +     /* Enable finish and error interrupts. */
> +     __raw_writeq(M_SMB_FINISH_INTR | M_SMB_ERR_INTR, csr + R_SMB_CONTROL);
> +
> +     /* Register new adapter to i2c module... */
> +     err = i2c_add_numbered_adapter(i2c_adap);
> +     if (err < 0)
> +             goto out_unirq;
> +
> +     return 0;
>  
> -     return i2c_add_numbered_adapter(i2c_adap);
> +out_unirq:
> +     /* Disable interrupts. */
> +     __raw_writeq(0, csr + R_SMB_CONTROL);
> +     mmiowb();
> +     __raw_readq(csr + R_SMB_CONTROL);
> +
> +     free_irq(adap->irq, i2c_adap);
> +
> +     /* Clear any pending error interrupt. */
> +     __raw_writeq(__raw_readq(csr + R_SMB_STATUS), csr + R_SMB_STATUS);

You may consider moving this block to a separate function, as it is
duplicated in the i2c_sibyte_remove_bus() function below.

> +out_unmap:
> +     iounmap(csr);
> +out:
> +     return err;
>  }
>  
> +static void i2c_sibyte_remove_bus(struct i2c_adapter *i2c_adap)
> +{
> +     struct i2c_algo_sibyte_data *adap = i2c_adap->algo_data;
> +     void __iomem *csr = adap->csr;
> +
> +     i2c_del_adapter(i2c_adap);
> +
> +     /* Disable interrupts. */
> +     __raw_writeq(0, csr + R_SMB_CONTROL);
> +     mmiowb();
> +     __raw_readq(csr + R_SMB_CONTROL);
>  
> -static struct i2c_algo_sibyte_data sibyte_board_data[2] = {
> -     { NULL, 0, (void *) (CKSEG1+A_SMB_BASE(0)) },
> -     { NULL, 1, (void *) (CKSEG1+A_SMB_BASE(1)) }
> +     free_irq(adap->irq, i2c_adap);
> +
> +     /* Clear any pending error interrupt. */
> +     __raw_writeq(__raw_readq(csr + R_SMB_STATUS), csr + R_SMB_STATUS);
> +
> +     iounmap(csr);
> +}
> +
> +static struct i2c_algo_sibyte_data i2c_sibyte_board_data[2] = {
> +#ifdef CONFIG_SIBYTE_SB1250
> +     {
> +             .name   = "sb1250-smbus-0",
> +             .base   = A_SMB_0,
> +             .irq    = K_INT_SMB_0,
> +     },
> +     {
> +             .name   = "sb1250-smbus-1",
> +             .base   = A_SMB_1,
> +             .irq    = K_INT_SMB_1,
> +     }
> +#else
> +     {
> +             .name   = "bcm1480-smbus-0",
> +             .base   = A_SMB_0,
> +             .irq    = K_BCM1480_INT_SMB_0,
> +     },
> +     {
> +             .name   = "bcm1480-smbus-1",
> +             .base   = A_SMB_1,
> +             .irq    = K_BCM1480_INT_SMB_1,
> +     }
> +#endif
>  };
>  
> -static struct i2c_adapter sibyte_board_adapter[2] = {
> +static struct i2c_adapter i2c_sibyte_board_adapter[2] = {
>       {
>               .owner          = THIS_MODULE,
>               .class          = I2C_CLASS_HWMON | I2C_CLASS_SPD,
> -             .algo           = NULL,
> -             .algo_data      = &sibyte_board_data[0],
> +             .algo           = &i2c_sibyte_algo,
> +             .algo_data      = &i2c_sibyte_board_data[0],
>               .nr             = 0,
>               .name           = "SiByte SMBus 0",
>       },
>       {
>               .owner          = THIS_MODULE,
>               .class          = I2C_CLASS_HWMON | I2C_CLASS_SPD,
> -             .algo           = NULL,
> -             .algo_data      = &sibyte_board_data[1],
> +             .algo           = &i2c_sibyte_algo,
> +             .algo_data      = &i2c_sibyte_board_data[1],
>               .nr             = 1,
>               .name           = "SiByte SMBus 1",
>       },
> @@ -173,21 +318,32 @@ static struct i2c_adapter sibyte_board_adapter[2] = {
>  
>  static int __init i2c_sibyte_init(void)
>  {
> +     int err;
> +
>       pr_info("i2c-sibyte: i2c SMBus adapter module for SiByte board\n");
> -     if (i2c_sibyte_add_bus(&sibyte_board_adapter[0], K_SMB_FREQ_100KHZ) < 0)
> -             return -ENODEV;
> -     if (i2c_sibyte_add_bus(&sibyte_board_adapter[1],
> -                            K_SMB_FREQ_400KHZ) < 0) {
> -             i2c_del_adapter(&sibyte_board_adapter[0]);
> -             return -ENODEV;
> -     }
> +
> +     err = i2c_sibyte_add_bus(&i2c_sibyte_board_adapter[0],
> +                              K_SMB_FREQ_100KHZ);
> +     if (err < 0)
> +             goto out;
> +
> +     err = i2c_sibyte_add_bus(&i2c_sibyte_board_adapter[1],
> +                              K_SMB_FREQ_400KHZ);
> +     if (err < 0)
> +             goto out_remove;
> +
>       return 0;
> +
> +out_remove:
> +     i2c_sibyte_remove_bus(&i2c_sibyte_board_adapter[0]);
> +out:
> +     return err;
>  }
>  
>  static void __exit i2c_sibyte_exit(void)
>  {
> -     i2c_del_adapter(&sibyte_board_adapter[0]);
> -     i2c_del_adapter(&sibyte_board_adapter[1]);
> +     i2c_sibyte_remove_bus(&i2c_sibyte_board_adapter[1]);
> +     i2c_sibyte_remove_bus(&i2c_sibyte_board_adapter[0]);
>  }
>  
>  module_init(i2c_sibyte_init);

Please address my concerns where you agree and send an updated patch.

-- 
Jean Delvare

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