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Re: [Alsa-devel] Au1550 OSS driver issues

To: linux-mips@linux-mips.org
Subject: Re: [Alsa-devel] Au1550 OSS driver issues
From: Sergei Shtylylov <sshtylyov@ru.mvista.com>
Date: Thu, 08 Dec 2005 22:40:50 +0300
Cc: dan@embeddededge.com, Jordan Crouse <jordan.crouse@amd.com>, Manish Lachwani <mlachwani@mvista.com>, Konstantin Baidarov <kbaidarov@ru.mvista.com>
In-reply-to: <436FB1DE.6010405@ru.mvista.com>
Organization: MostaVista Software Inc.
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <43452054.2090305@ru.mvista.com> <436FB1DE.6010405@ru.mvista.com>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mozilla/5.0 (X11; U; Linux i686; rv:1.7.2) Gecko/20040803
Hello, I wrote:

    We have found some issues with Au1550 AC'97 OSS driver in 2.6
(sound/oss/au1550_ac97.c), though it also should concern 2.4 driver
(drivers/sound/au1550_psc.c).

[au_readl() issue skipped]

Second, start_dac() grabs a spinlock already held by its caller, au1550_write(). This doesn't show up with the standard UP spinlock impelmentation but when the different one (mutex based) is in use, a lockup happens. The second patch demonstates a possible solution but here's a question: why there's no "symmetric" spinlock logic in start_adc(), may be here exits another potential issue?

   Unfortunately, the proposed solution was incorrect for that mutex case
because it was breaking the "critical section" by temporarily dropping the
spinlock to call start_dac(). So, here's the updated version of that patch in
which start_dac() and start_adc() don't grab the spinlocks anymore but their
callers do instead.

        After having a look at sound/oss/au1000.c,

   Now I don't think that this trick is always correct but since that driver
is obsoleted by ALSA one I don't care that much. ;-)

here's an updated patch that deals with "nested" spinlocks the same way that driver does, and adds spinlock to start_adc() as well.

   And the interrupt handlers also didn't grab the spinlock -- that's OK
in the usual kernel but not when the IRQ handlers are threaded. So, they're
grabbing the spinlock now (as every correct interrupt handler should do).

WBR, Sergei


diff --git a/sound/oss/au1550_ac97.c b/sound/oss/au1550_ac97.c
index cdce915..f70effd 100644
--- a/sound/oss/au1550_ac97.c
+++ b/sound/oss/au1550_ac97.c
@@ -579,17 +579,15 @@ set_recv_slots(int num_channels)
        } while ((stat & PSC_AC97STAT_DR) == 0);
 }
 
+/* Hold spinlock for both start_dac() and start_adc() calls */
 static void
 start_dac(struct au1550_state *s)
 {
        struct dmabuf  *db = &s->dma_dac;
-       unsigned long   flags;
 
        if (!db->stopped)
                return;
 
-       spin_lock_irqsave(&s->lock, flags);
-
        set_xmit_slots(db->num_channels);
        au_writel(PSC_AC97PCR_TC, PSC_AC97PCR);
        au_sync();
@@ -599,8 +597,6 @@ start_dac(struct au1550_state *s)
        au1xxx_dbdma_start(db->dmanr);
 
        db->stopped = 0;
-
-       spin_unlock_irqrestore(&s->lock, flags);
 }
 
 static void
@@ -719,7 +715,6 @@ prog_dmabuf_dac(struct au1550_state *s)
 }
 
 
-/* hold spinlock for the following */
 static void
 dac_dma_interrupt(int irq, void *dev_id, struct pt_regs *regs)
 {
@@ -727,6 +722,8 @@ dac_dma_interrupt(int irq, void *dev_id,
        struct dmabuf  *db = &s->dma_dac;
        u32     ac97c_stat;
 
+       spin_lock(&s->lock);
+
        ac97c_stat = au_readl(PSC_AC97STAT);
        if (ac97c_stat & (AC97C_XU | AC97C_XO | AC97C_TE))
                pr_debug("AC97C status = 0x%08x\n", ac97c_stat);
@@ -748,6 +745,8 @@ dac_dma_interrupt(int irq, void *dev_id,
        /* wake up anybody listening */
        if (waitqueue_active(&db->wait))
                wake_up(&db->wait);
+
+       spin_unlock(&s->lock);
 }
 
 
@@ -759,6 +758,8 @@ adc_dma_interrupt(int irq, void *dev_id,
        u32     obytes;
        char    *obuf;
 
+       spin_lock(&s->lock);
+
        /* Pull the buffer from the dma queue.
        */
        au1xxx_dbdma_get_dest(dp->dmanr, (void *)(&obuf), &obytes);
@@ -766,6 +767,7 @@ adc_dma_interrupt(int irq, void *dev_id,
        if ((dp->count + obytes) > dp->dmasize) {
                /* Overrun. Stop ADC and log the error
                */
+               spin_unlock(&s->lock);
                stop_adc(s);
                dp->error++;
                err("adc overrun");
@@ -788,6 +790,7 @@ adc_dma_interrupt(int irq, void *dev_id,
        if (waitqueue_active(&dp->wait))
                wake_up(&dp->wait);
 
+       spin_unlock(&s->lock);
 }
 
 static loff_t
@@ -1049,9 +1052,9 @@ au1550_read(struct file *file, char *buf
                /* wait for samples in ADC dma buffer
                */
                do {
+                       spin_lock_irqsave(&s->lock, flags);
                        if (db->stopped)
                                start_adc(s);
-                       spin_lock_irqsave(&s->lock, flags);
                        avail = db->count;
                        if (avail <= 0)
                                __set_current_state(TASK_INTERRUPTIBLE);
@@ -1571,15 +1574,19 @@ au1550_ioctl(struct inode *inode, struct
                if (get_user(val, (int *) arg))
                        return -EFAULT;
                if (file->f_mode & FMODE_READ) {
-                       if (val & PCM_ENABLE_INPUT)
+                       if (val & PCM_ENABLE_INPUT) {
+                               spin_lock_irqsave(&s->lock, flags);
                                start_adc(s);
-                       else
+                               spin_unlock_irqrestore(&s->lock, flags);
+                       } else
                                stop_adc(s);
                }
                if (file->f_mode & FMODE_WRITE) {
-                       if (val & PCM_ENABLE_OUTPUT)
+                       if (val & PCM_ENABLE_OUTPUT) {
+                               spin_lock_irqsave(&s->lock, flags);
                                start_dac(s);
-                       else
+                               spin_unlock_irqrestore(&s->lock, flags);
+                       } else
                                stop_dac(s);
                }
                return 0;



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