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

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Message-ID: <498a99e1-77ca-4acf-8850-cb74417ae88c@xs4all.nl>
Date: Wed, 8 Jan 2025 08:47:41 +0100
From: Hans Verkuil <hverkuil@...all.nl>
To: Dikshita Agarwal <quic_dikshita@...cinc.com>,
 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 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.

Regards,

	Hans

> 
> Thanks,
> Dikshita
>> Nicolas
>>
>>>
>>> Thanks,
>>> Dikshita
>>>> Thanks,
>>>> Mauro
>>