linux-kernel - Re: [PATCH v2 07/11] PCI/VGA: vga_client_register() return -ENODEV on failure, not -1

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Date:   Thu, 10 Aug 2023 19:56:26 +0800
From:   suijingfeng <suijingfeng@...ngson.cn>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        Sui Jingfeng <sui.jingfeng@...ux.dev>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Dave Airlie <airlied@...hat.com>,
        Daniel Vetter <daniel@...ll.ch>, linux-pci@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 07/11] PCI/VGA: vga_client_register() return -ENODEV on
 failure, not -1

Hi,


On 2023/8/9 21:52, Ilpo Järvinen wrote:
> On Wed, 9 Aug 2023, Sui Jingfeng wrote:
>
>> From: Sui Jingfeng <suijingfeng@...ngson.cn>
>>
> Changelog body is missing.


I thought that probably the Fixes tag could be taken as the body of this commit,
since there are no warnings when I check the whole series with checkpatch.pl.


>> Fixes: 934f992c763a ("drm/i915: Recognise non-VGA display devices")
>> Signed-off-by: Sui Jingfeng <suijingfeng@...ngson.cn>
>> ---
>>   drivers/pci/vgaarb.c | 15 ++++++---------
>>   1 file changed, 6 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c
>> index 811510253553..a6b8c0def35d 100644
>> --- a/drivers/pci/vgaarb.c
>> +++ b/drivers/pci/vgaarb.c
>> @@ -964,7 +964,7 @@ EXPORT_SYMBOL(vga_set_legacy_decoding);
>>    *
>>    * To unregister just call vga_client_unregister().
>>    *
>> - * Returns: 0 on success, -1 on failure
>> + * Returns: 0 on success, -ENODEV on failure
> So this is the true substance of this change??
>
Yes.


> It doesn't warrant Fixes tag which requires a real problem to fix. An
> incorrect comment is not enough.
>
> I think the shortlog is a bit misleading as is because it doesn't in any
> way indicate the problem is only in a comment.

But it's that commit(934f992c763a) alter the return value of vga_client_register(),
which make the commit and code don't match anymore.


>>    */
>>   int vga_client_register(struct pci_dev *pdev,
>>   		unsigned int (*set_decode)(struct pci_dev *pdev, bool decode))
>> @@ -975,16 +975,13 @@ int vga_client_register(struct pci_dev *pdev,
>>   
>>   	spin_lock_irqsave(&vga_lock, flags);
>>   	vgadev = vgadev_find(pdev);
>> -	if (!vgadev)
>> -		goto bail;
>> -
>> -	vgadev->set_decode = set_decode;
>> -	ret = 0;
>> -
>> -bail:
>> +	if (vgadev) {
>> +		vgadev->set_decode = set_decode;
>> +		ret = 0;
>> +	}
>>   	spin_unlock_irqrestore(&vga_lock, flags);
>> -	return ret;
>>   
>> +	return ret;
> No logic changes in this at all? I don't think it belongs to the same
> patch. I'm not sure if the new logic is improvement anyway.


Yes, the new logic is just improvement, no function change.
Strict speaking, you are right. One patch do one thing.


>   I'd prefer to
> initialize ret = 0 instead:
>
> 	int ret = 0;
> 	...
> 	if (!vgadev) {
> 		err = -ENODEV;
> 		goto unlock;
> 	}
> 	...
> unlock:
> 	...
>

But this is same as the original coding style, no fundamental improve.
The key point is to make the wrapped code between the spin_lock_irqsave() and spin_unlock_irqrestore() compact.
my patch remove the necessary 'goto' statement and the 'bail' label.
After apply my patch, the vga_client_register() function became as this:

int vga_client_register(struct pci_dev *pdev,
         unsigned int (*set_decode)(struct pci_dev *pdev, bool decode))
{
     int ret = -ENODEV;
     struct vga_device *vgadev;
     unsigned long flags;

     spin_lock_irqsave(&vga_lock, flags);
     vgadev = vgadev_find(pdev);
     if (vgadev) {
         vgadev->set_decode = set_decode;
         ret = 0;
     }
     spin_unlock_irqrestore(&vga_lock, flags);

     return ret;
}