linux-kernel - Re: [PATCH v9 27/28] media: iris: enable video driver probe of SM8250 SoC

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Message-ID: <9fc76dd1-ef49-a9d2-0271-eacb50943b03@quicinc.com>
Date: Wed, 8 Jan 2025 14:21:16 +0530
From: Dikshita Agarwal <quic_dikshita@...cinc.com>
To: Hans Verkuil <hverkuil@...all.nl>,
        Nicolas Dufresne
	<nicolas@...fresne.ca>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Sebastian Fricke <sebastian.fricke@...labora.com>
CC: Vikash Garodia <quic_vgarodia@...cinc.com>,
        Abhinav Kumar
	<quic_abhinavk@...cinc.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        "Rob
 Herring" <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        "Conor
 Dooley" <conor+dt@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        "Bryan
 O'Donoghue" <bryan.odonoghue@...aro.org>,
        Dmitry Baryshkov
	<dmitry.baryshkov@...aro.org>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Uwe Kleine-König <u.kleine-koenig@...libre.com>,
        Jianhua Lu
	<lujianhua000@...il.com>,
        Stefan Schmidt <stefan.schmidt@...aro.org>,
        <linux-media@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9 27/28] media: iris: enable video driver probe of SM8250
 SoC



On 1/8/2025 1:17 PM, Hans Verkuil wrote:
> On 08/01/2025 08:43, Dikshita Agarwal wrote:
>>
>>
>> On 1/7/2025 7:27 PM, Nicolas Dufresne wrote:
>>> Le lundi 23 décembre 2024 à 16:21 +0530, Dikshita Agarwal a écrit :
>>>>
>>>> On 12/23/2024 4:00 PM, Mauro Carvalho Chehab wrote:
>>>>> Em Thu, 12 Dec 2024 17:21:49 +0530
>>>>> Dikshita Agarwal <quic_dikshita@...cinc.com> escreveu:
>>>>>
>>>>>> +	.dma_mask = GENMASK(31, 29) - 1,
>>>>>
>>>>> Setting a mask to GENMASK() - 1 sounds weird. Is it really what you want?
>>>>> I so, why?
>>>>>
>>>> Hi Mauro,
>>>>
>>>> the value of this dma mask should be 0xe0000000 -1.
>>>>
>>>> The background for the same is, 0xe0000000 onward memory space is allocated
>>>> for IO register space so we are restricting the driver buffer allocations
>>>> to 0xe0000000 - 1.
>>>>
>>>> Based on the comments received in the past, we are using GENMASK to
>>>> generate 0xe0000000.
>>>>
>>>> Does this answer your query or I missed something?
>>>
>>> I'm not sure it will do what you want. (0xe0000000 -1) matches ~BIT(29). Perhaps
>>> you wanted to use ~0xe0000000. 
>>>
>> value of dma mask is coming as expected with GENMASK(31, 29) - 1
>>
>> qcom-iris aa00000.video-codec: dma_mask DFFFFFFF (0xe0000000 -1)
> 
> Isn't this just the equivalent of GENMASK(28, 0)? Can't you use that?
> 
> It's much easier to understand than GENMASK()-1.

Sure, I can use either ~GENMASK(29, 29) or ~BIT(29),
Please let me know which would be better?

Thanks,
Dikshita

> 
> Regards,
> 
> 	Hans
> 
>>
>> Thanks,
>> Dikshita
>>> Nicolas
>>>
>>>>
>>>> Thanks,
>>>> Dikshita
>>>>> Thanks,
>>>>> Mauro
>>>
> 
>