linux-kernel - Re: [PATCH] media: hantro: fix compatible string deprecation warning

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Date:   Thu, 9 Jun 2022 10:47:26 +0200
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Robin Murphy <robin.murphy@....com>,
        Martin Kepplinger <martin.kepplinger@...i.sm>,
        ezequiel@...guardiasur.com.ar, p.zabel@...gutronix.de,
        mchehab@...nel.org
Cc:     linux-media@...r.kernel.org, linux-rockchip@...ts.infradead.org,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: hantro: fix compatible string deprecation warning

Hi Martin,

On 5/17/22 18:46, Robin Murphy wrote:
> On 2022-05-17 15:35, Martin Kepplinger wrote:
>> of_device_is_compatible() in the end uses strlen of the string
>> for comparison, so in this case, the condition is true even if
>> the requested string "nxp,imx8mq-vpu-g1" is being used. The first
>> chars containing "nxp,imx8mq-vpu" are the same.
> 
> Have you seen this go wrong in practice? AFAICS, unless you're on SPARC, which seems somewhat unlikely for an i.MX8 peripheral, of_compat_cmp() should map to strcasecmp(), which should do the right thing :/

Robin is correct, the existing code is fine for all but SPARC, which
won't be using this driver.

I'm rejecting this patch.

Regards,

	Hans

> 
> Robin.
> 
>> Fix this by encoding what the comment says.
>>
>> Signed-off-by: Martin Kepplinger <martin.kepplinger@...i.sm>
>> ---
>>
>> This is more of a bugreport as the solution doesn't look very elegant
>> to me. I'm happy for advice.
>>
>> thanks,
>>                             martin
>>
>>
>>   drivers/staging/media/hantro/hantro_drv.c | 7 ++++---
>>   1 file changed, 4 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/staging/media/hantro/hantro_drv.c b/drivers/staging/media/hantro/hantro_drv.c
>> index ac232b5f7825..014fab637df0 100644
>> --- a/drivers/staging/media/hantro/hantro_drv.c
>> +++ b/drivers/staging/media/hantro/hantro_drv.c
>> @@ -923,10 +923,11 @@ static int hantro_probe(struct platform_device *pdev)
>>         /*
>>        * Support for nxp,imx8mq-vpu is kept for backwards compatibility
>> -     * but it's deprecated. Please update your DTS file to use
>> -     * nxp,imx8mq-vpu-g1 or nxp,imx8mq-vpu-g2 instead.
>> +     * but it's deprecated.
>>        */
>> -    if (of_device_is_compatible(pdev->dev.of_node, "nxp,imx8mq-vpu"))
>> +    if ((of_device_is_compatible(pdev->dev.of_node, "nxp,imx8mq-vpu")) &&
>> +        (!of_device_is_compatible(pdev->dev.of_node, "nxp,imx8mq-vpu-g1")) &&
>> +        (!of_device_is_compatible(pdev->dev.of_node, "nxp,imx8mq-vpu-g2")))
>>           dev_warn(&pdev->dev, "%s compatible is deprecated\n",
>>                match->compatible);
>>