Re: [PATCH] Revert "backlight: pwm: Handle EPROBE_DEFER while requesting the PWM"

Robert Jarzmik
2015-10-01T09:11:49Z

Nicolas Ferre <nicolas.ferre@atmel.com> writes:

> Le 30/09/2015 21:29, Robert Jarzmik a écrit :
>> Robert Jarzmik <robert.jarzmik@free.fr> writes:
>>
>>> This reverts commit 68feaca0b13e453aa14ee064c1736202b48b342f.
>>> This commit breaks legacy platforms, for which :
>>> (a) no pwm table is added (legacy platforms)
>>> (b) in this case, in pwm_get(), pmw_lookup_list is empty, and therefore
>>> chosen == NULL, and therefore pwm_get() returns NULL, and pwm_get()
>>> returns -EPROBE_DEFER
>>> (c) as a consequence, this code is unreachable in pwm_bl.c :
>>> if (IS_ERR(pb->pwm)) {
>>> ret = PTR_ERR(pb->pwm);
>>> dev_info(&pdev->dev, "%s:%d(): %d\n", __func__, __LINE__, ret);
>>> if (ret == -EPROBE_DEFER)
>>> goto err_alloc;
>>>
>>> dev_err(&pdev->dev, "unable to request PWM, trying legacy API\n");
>>> pb->legacy = true;
>>> pb->pwm = pwm_request(data->pwm_id, "pwm-backlight");
>>>
>>> As this code is unreachable, all legacy platforms relying on pwm_id are
>>> broken, amongst which pxa have been tested as broken.
>>>
>>> Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
>> Thierry, would you have a look please ?
>> As I said before, all legacy platform relying on pwm_id are broken. I'd like to
>> be sure this lands in the next -rc series.
>
> Well, as I answered on the linux-pwm mailing-list (I was not in copy) here:
> http://article.gmane.org/gmane.linux.pwm/2744
> I wonder if it's not easier to fix the platforms and add the pwm tables...
No it's not, at least not for a -rc cycle. It's the long term solution you're
talking about, not the fix one.

> Otherwise, Boris proposed this fix:
> 8<-----------------------------------------------------------
> diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
> index eff379b..00483d4 100644
> --- a/drivers/video/backlight/pwm_bl.c
> +++ b/drivers/video/backlight/pwm_bl.c
> @@ -273,15 +273,15 @@ static int pwm_backlight_probe(struct platform_device *pdev)
> pb->pwm = devm_pwm_get(&pdev->dev, NULL);
> if (IS_ERR(pb->pwm)) {
> ret = PTR_ERR(pb->pwm);
> - if (ret == -EPROBE_DEFER)
> - goto err_alloc;
>
> dev_err(&pdev->dev, "unable to request PWM, trying legacy API\n");
> pb->legacy = true;
> pb->pwm = pwm_request(data->pwm_id, "pwm-backlight");
> if (IS_ERR(pb->pwm)) {
> dev_err(&pdev->dev, "unable to request legacy PWM\n");
> - ret = PTR_ERR(pb->pwm);
> + if (ret != -EPROBE_DEFER)
> + ret = PTR_ERR(pb->pwm);
> +
> goto err_alloc;
> }
> }
>
> which is not tested and may add an extra non-valid error log.
I can test that, today, it looks an interesting alternative.

If both solutions do work, someone (Boris) can post a patch for this -rc instead
of the revert. If no patch is posted, I maintain my Revert, as this patch _does_
break platforms (omap is broken too AFAICS).

Cheers.

--
Robert

PS: I have not received http://article.gmane.org/gmane.linux.pwm/2744.
Is it my mailer or MUA which is broken, ie. was I in the "To:" of the mail ?

PPS: Sorry to having forgotten to join you to the revert

PPPS: As long as an other patch is not submitted to fix the issue (other than
the Revert), I NAK the NAK. There is a breakage introduced, and I consider
it a strong enough reason to be maintained for the -rc serie.