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

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Message-ID: <5953bea1-194d-fe2e-251a-d4ef3e7544d3@quicinc.com>
Date: Wed, 8 Jan 2025 16:42:03 +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 4:13 PM, Hans Verkuil wrote:
> On 1/8/25 11:21, Dikshita Agarwal wrote:
>>
>>
>> On 1/8/2025 2:25 PM, Hans Verkuil wrote:
>>> On 08/01/2025 09:51, Dikshita Agarwal wrote:
>>>>
>>>>
>>>> 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?
>>>
>>> Too early in the morning, this suggestion was clearly wrong.
>>>
>>>>>
>>>>> It's much easier to understand than GENMASK()-1.
>>>>
>>>> Sure, I can use either ~GENMASK(29, 29) or ~BIT(29),
>>>
>>> ~BIT(29).
>>>
>>> It's really weird to just disable a single bit, so I think some comments
>>> explaining why this mask is needed would be good (if there aren't comments
>>> already).
>>>
>> I tested this some more, and seems ~BIT(29) doesn't work, as its still
>> conflicting with the register space.
> 
> Odd, perhaps a 64 vs 32 bit issue?
> 
>> Correct value would be GENMASK(31,30) + GENMASK(28,0) to set the exact bits
>> to get the desired value i.e 0xe0000000 -1
> 
> Honestly, in this case I would prefer to just go with the actual hex value
> 0xdfffffff together with an explanatory comment.
> 
We moved to GENMASK way to address comment on previous version, but sure
can directly use 0xdfffffff with a comment.

Thanks,
Dikshita
> Regards,
> 
> 	Hans
> 
>>> Regards,
>>>
>>> 	Hans
>>>
>>>> Please let me know which would be better?
>>>>
>>>> Thanks,
>>>> Dikshita
>>>>
>>>>>
>>>>> Regards,
>>>>>
>>>>> 	Hans
>>>>>
>>>>>>
>>>>>> Thanks,
>>>>>> Dikshita
>>>>>>> Nicolas
>>>>>>>
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> Dikshita
>>>>>>>>> Thanks,
>>>>>>>>> Mauro
>>>>>>>
>>>>>
>>>>>
>>>
>