linux-kernel - Re: [PATCH 09/13] media: qcom: camss: Add CSID Gen3 support for SM8550

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Message-ID: <08b57750-536c-4dbb-9688-fa0622b0bbb3@kernel.org>
Date: Thu, 11 Jul 2024 14:17:35 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
 Depeng Shao <quic_depengs@...cinc.com>, rfoss@...nel.org,
 todor.too@...il.com, mchehab@...nel.org, robh@...nel.org,
 krzk+dt@...nel.org, conor+dt@...nel.org
Cc: quic_eberman@...cinc.com, linux-media@...r.kernel.org,
 linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, kernel@...cinc.com,
 Yongsheng Li <quic_yon@...cinc.com>
Subject: Re: [PATCH 09/13] media: qcom: camss: Add CSID Gen3 support for
 SM8550

On 11/07/2024 14:00, Bryan O'Donoghue wrote:
> On 11/07/2024 12:41, Depeng Shao wrote:
>>>> Yes, these are some sequences to initialize the HW.
>>>
>>> Hm? It's like you ignore the problem and just answer with whatever to
>>> shut up the reviewer. Instead of replying with the same, address the
>>> problem. Why ordering is not a problem here?
>>>
>>
>> Sorry, I didn't mean that, was trying to understand the problem, then 
>> just sent out the mail by mistake.
>> Do you mean we should use writel to ensure the strict sequences?
>> Thanks for catching this problem, this problem is also in the the 
>> existing camss driver. I will check all of them in this series, but the 
>> problem in some existing camss drivers, maybe Bryan from Linaro can help 
>> to fix them, since I don't have these devices to verify the modifications.
> 
> _relaxed is used I'm sure because that's what's always been used and 
> what downstream does.
> 
> Is there a good reason for it ? None that I can think of.
> 
> Krzysztof is right, there's no good reason to use relaxed() here at all, 
> you should drop it.
> 

In many cases relaxed will be fine, but in few might lead to tricky to
debug issues thus people introducing msleep() or other workarounds.
Usually init sequences are "sequences" for a reason, but of course here
maybe it does not matter.

Best regards,
Krzysztof