linux-kernel - Re: [PATCH] drm/irq: Add irq as false detection

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Date:   Mon, 2 Nov 2020 13:40:15 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Tian Tao <tiantao6@...ilicon.com>,
        maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
        airlied@...ux.ie, daniel@...ll.ch, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/irq: Add irq as false detection

Hi

Am 02.11.20 um 13:09 schrieb Thomas Zimmermann:
> Hi
> 
> Am 02.11.20 um 12:19 schrieb Tian Tao:
>> Add the detection of false for irq, so that the EINVAL is not
>> returned when dev->irq_enabled is false.
>>
>> Signed-off-by: Tian Tao <tiantao6@...ilicon.com>
>> ---
>>  drivers/gpu/drm/drm_irq.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
>> index 09d6e9e..7537a3d 100644
>> --- a/drivers/gpu/drm/drm_irq.c
>> +++ b/drivers/gpu/drm/drm_irq.c
>> @@ -172,6 +172,9 @@ int drm_irq_uninstall(struct drm_device *dev)
>>  	bool irq_enabled;
>>  	int i;
>>  
>> +	if (!dev->irq_enabled || !dev)
>> +		return 0;
>> +
> 
> Dereferencing a pointer before NULL-checking it, is Yoda programming. :)
> I'd just drop the test for !dev and assume that dev is always valid.
> 
> I suggest to change the int return value to void and return nothing.
> 
> Re-reading the actual implementation of this function, this location
> might be too early. Further below there already is a test for
> irq_enabled. Put a drm_WARN_ON around it and it should be fine. This way
> the vblank handlers will be disabled and erroneous callers will see a
> warning in the kernel's log.

In addition to these changes, you could also add a managed
implementation of drm_irq_install(). The canonical name should be
devm_drm_irq_install(). The function would call drm_irq_install() and
register a cleanup handler via devm_add_action(). Example code is at [1].

KMS drivers, such as hibmc, would then not have to bother about
uninstalling the DRM irq.

Best regards
Thomas

[1]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpu/drm/drm_drv.c#n664

> 
> Best regards
> Thomas
> 
>>  	irq_enabled = dev->irq_enabled;
>>  	dev->irq_enabled = false;
>>  
>>
> 
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@...ts.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer

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