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Re: [PATCH 0/3] MIPS: JZ4740: Move PWM driver to PWM framework

To: Thierry Reding <>
Subject: Re: [PATCH 0/3] MIPS: JZ4740: Move PWM driver to PWM framework
From: Maarten ter Huurne <>
Date: Sun, 02 Sep 2012 15:25:55 +0200
Cc: Ralf Baechle <>,,, Antony Pavlov <>, Lars-Peter Clausen <>
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On Sunday 02 September 2012 11:52:27 Thierry Reding wrote:

> This small series fixes a build error due to a circular header
> dependency, exports the timer API so it can be used outside of
> the arch/mips/jz4740 tree and finally moves and converts the
> JZ4740 PWM driver to the PWM framework.
> Note that I don't have any hardware to test this on, so I had to
> rely on compile tests only. Patches 1 and 2 should probably go
> through the MIPS tree, while I can take patch 3 through the PWM
> tree. It touches a couple of files in arch/mips but the changes
> are unlikely to cause conflicts.

Exporting the hardware outputs PWM2-7 as index 0-5 in the PWM core is rather 
confusing. I discussed with Lars on IRC and it's probably better to expose 
PWM0-7 through the API, but refuse to hand out PWM0 and PWM1 when requested, 
since their associated timers are in use by the system. I attached a diff 
that illustrates this approach.

Note that if this approach is taken, the beeper ID in board-qi_lb60.c should 
be changed back from 2 to 4, since the beeper is attached to PWM4.

I tested the "for-next" branch on the Dingoo A320 with the pwm-backlight 
driver. It didn't work at first, because the PWM number and the timer number 
didn't align: I requested PWM number 5 to get PWM7 and the GPIO of PWM7 was 
used, but with timer 5 instead of timer 7, resulting in a dark screen. 
However, it works fine after adding PWM0/1 as described above.

If other people want to test on real hardware, you can find the code in 
branch jz-3.6-rc2-pwm in the qi-kernel repository. Unfortunately our web 
interface for git is still broken, but the repo itself is fine.

diff --git a/drivers/pwm/pwm-jz4740.c b/drivers/pwm/pwm-jz4740.c
index db29b37..554e414 100644
--- a/drivers/pwm/pwm-jz4740.c
+++ b/drivers/pwm/pwm-jz4740.c
@@ -24,9 +24,11 @@
 #include <asm/mach-jz4740/gpio.h>
 #include <timer.h>
-#define NUM_PWM 6
+#define NUM_PWM 8
 static const unsigned int jz4740_pwm_gpio_list[NUM_PWM] = {
+       JZ_GPIO_PWM0,
+       JZ_GPIO_PWM1,
@@ -50,6 +52,13 @@ static int jz4740_pwm_request(struct pwm_chip *chip, struct 
pwm_device *pwm)
        unsigned int gpio = jz4740_pwm_gpio_list[pwm->hwpwm];
        int ret;
+       /*
+        * Timer 0 and 1 are used for system tasks, so they are unavailable
+        * for use as PWMs.
+        */
+       if (pwm->hwpwm < 2)
+               return -EBUSY;
        ret = gpio_request(gpio, pwm->label);
        if (ret) {
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