linux-kernel - Re: [PATCH] drm/hisilicon: Remove redundant null check

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Date:   Mon, 2 Nov 2020 10:03:39 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     "tiantao (H)" <tiantao6@...wei.com>,
        Tian Tao <tiantao6@...ilicon.com>, airlied@...ux.ie,
        daniel@...ll.ch, kraxel@...hat.com, alexander.deucher@....com,
        tglx@...utronix.de, dri-devel@...ts.freedesktop.org,
        xinliang.liu@...aro.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/hisilicon: Remove redundant null check

Hi

Am 02.11.20 um 09:46 schrieb tiantao (H):
> 
> 
> 在 2020/11/2 16:32, Thomas Zimmermann 写道:
>> Hi
>>
>> Am 30.10.20 um 10:27 schrieb Tian Tao:
>>> drm_irq_uninstall can handle the case where dev->irq_enable is false,
>>> so Remove redundant null check.
>>>
>>> Signed-off-by: Tian Tao <tiantao6@...ilicon.com>
>>> ---
>>>   drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_drv.c | 6 +++---
>>>   1 file changed, 3 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_drv.c
>>> b/drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_drv.c
>>> index 0c1b40d..b71589b1 100644
>>> --- a/drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_drv.c
>>> +++ b/drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_drv.c
>>> @@ -246,13 +246,13 @@ static int hibmc_unload(struct drm_device *dev)
>>>         drm_atomic_helper_shutdown(dev);
>>>   -    if (dev->irq_enabled)
>>> -        drm_irq_uninstall(dev);
>>> -
>>> +    drm_irq_uninstall(dev);
>>
>> Removing this check would at least result in an error, [1] so rather
>> leave it in for now.
>>
> Now there seems to be no driver to check the return value of
> drm_irq_uninstall

True. No clean-up code should ever fail. But currently, it's not handled
by drm_irq_uninstall().

A better fix would be to have drm_irq_uninstall() return early with a
warning if IRQs are disabled. And for most drivers, a managed version of
drm_irq_install() would be useful.

Best regards
Thomas

>> Instead, we could discuss if drm_irq_install() should become a managed
>> interface.
> 
> Codes like the following
> diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
> index 09d6e9e..572357c 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;
> 
>>
>> Best regards
>> Thomas
>>
>> [1]
>> https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_irq.c#L201
>>
>>
>>>       pci_disable_msi(dev->pdev);
>>> +
>>>       hibmc_kms_fini(priv);
>>>       hibmc_mm_fini(priv);
>>>       dev->dev_private = NULL;
>>> +
>>>       return 0;
>>>   }
>>>  
>>
> 

-- 
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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