linux-kernel - Re: [PATCH] drm/bridge: tpd12s015: Fix irq registering in tpd12s015

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Message-ID: <bbf82393-0cbd-bb2c-6002-368486a1b900@ti.com>
Date:   Mon, 2 Nov 2020 11:42:10 +0200
From:   Tomi Valkeinen <tomi.valkeinen@...com>
To:     Yuehaibing <yuehaibing@...wei.com>, Sam Ravnborg <sam@...nborg.org>
CC:     <a.hajda@...sung.com>, <narmstrong@...libre.com>,
        <Laurent.pinchart@...asonboard.com>, <jonas@...boo.se>,
        <jernej.skrabec@...l.net>, <airlied@...ux.ie>, <daniel@...ll.ch>,
        <sebastian.reichel@...labora.com>,
        <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/bridge: tpd12s015: Fix irq registering in
 tpd12s015_probe

On 02/11/2020 11:36, Yuehaibing wrote:
> On 2020/11/2 14:57, Tomi Valkeinen wrote:
>> On 31/10/2020 09:19, Sam Ravnborg wrote:
>>> Hi YueHaibing
>>>
>>> Thanks for the fix. Appreciated but please update as per comments below.
>>>
>>> On Sat, Oct 31, 2020 at 11:16:48AM +0800, YueHaibing wrote:
>>>> gpiod_to_irq() return negative value in case of error,
>>>> the existing code handle negative error codes wrongly.
>>>>
>>>> Fixes: cff5e6f7e83f ("drm/bridge: Add driver for the TI TPD12S015 HDMI level shifter")
>>>> Signed-off-by: YueHaibing <yuehaibing@...wei.com>
>>>> ---
>>>>  drivers/gpu/drm/bridge/ti-tpd12s015.c | 2 +-
>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/bridge/ti-tpd12s015.c b/drivers/gpu/drm/bridge/ti-tpd12s015.c
>>>> index 514cbf0eac75..a18d5197c16c 100644
>>>> --- a/drivers/gpu/drm/bridge/ti-tpd12s015.c
>>>> +++ b/drivers/gpu/drm/bridge/ti-tpd12s015.c
>>>> @@ -160,7 +160,7 @@ static int tpd12s015_probe(struct platform_device *pdev)
>>>>  
>>>>  	/* Register the IRQ if the HPD GPIO is IRQ-capable. */
>>>>  	tpd->hpd_irq = gpiod_to_irq(tpd->hpd_gpio);
>>>> -	if (tpd->hpd_irq) {
>>>> +	if (tpd->hpd_irq > 0) {
>>>>  		ret = devm_request_threaded_irq(&pdev->dev, tpd->hpd_irq, NULL,
>>>>  						tpd12s015_hpd_isr,
>>>>  						IRQF_TRIGGER_RISING |
>>>
>>> The current implmentation will skip devm_request_threaded_irq() in case
>>> or error - but continue with the rest of the function. So the
>>> driver fails to return an error code.
>>
>> That is intended. If the HPD gpio supports IRQs (gpiod_to_irq returns a valid number), we use the
>> IRQ. If it doesn't (gpiod_to_irq returns an error), it gets polled via detect(). Both are ok.
>>
>> I don't know if the gpiod_to_irq never returning 0 is something we should rely on. The docs say
>> gpiod_to_irq returns the irq number or an error, so I think checking for >= 0 matches the docs better.
>>
> 
> gpiod_to_irq() now never returns 0, see:
> https://elixir.bootlin.com/linux/v5.10-rc2/source/drivers/gpio/gpiolib.c#L3183
> 
> Also commit 4c37ce8608a8 ("gpio: make gpiod_to_irq() return negative for NO_IRQ") says:
> 
> commit 4c37ce8608a8c6521726d4cd1d4f54424e8d095f
> Author: Linus Walleij <linus.walleij@...aro.org>
> Date:   Mon May 2 13:13:10 2016 +0200
> 
>     gpio: make gpiod_to_irq() return negative for NO_IRQ
> 
>     If a translation returns zero, that means NO_IRQ, so we
>     should return an error since the function is documented to
>     return a negative code on error.
> 
> So checking for >0 is enough, my patch is correct.

Yes, but that is a gpiod_to_irq internal implementation detail. The documentation says it returns an
error code (negative) or a valid irq number. The documentation does not say gpiod_to_irq never
returns 0.

 Tomi

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