linux-kernel - Re: [PATCH V21 2/7] soc: qcom: dcc: Add driver support for Data Capture and Compare unit(DCC)

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Message-ID: <20221228172825.r32vpphbdulaldvv@builder.lan>
Date:   Wed, 28 Dec 2022 11:28:25 -0600
From:   Bjorn Andersson <andersson@...nel.org>
To:     Souradeep Chowdhury <quic_schowdhu@...cinc.com>
Cc:     Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Herring <robh+dt@...nel.org>, Alex Elder <elder@...e.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        Sai Prakash Ranjan <quic_saipraka@...cinc.com>,
        Sibi Sankar <quic_sibis@...cinc.com>,
        Rajendra Nayak <quic_rjendra@...cinc.com>, vkoul@...nel.org
Subject: Re: [PATCH V21 2/7] soc: qcom: dcc: Add driver support for Data
 Capture and Compare unit(DCC)

On Tue, Dec 27, 2022 at 08:52:46PM +0530, Souradeep Chowdhury wrote:
> The DCC is a DMA Engine designed to capture and store data
> during system crash or software triggers. The DCC operates
> based on user inputs via the debugfs interface. The user gives
> addresses as inputs and these addresses are stored in the
> dcc sram. In case of a system crash or a manual software
> trigger by the user through the debugfs interface,
> the dcc captures and stores the values at these addresses.
> This patch contains the driver which has all the methods
> pertaining to the debugfs interface, auxiliary functions to
> support all the four fundamental operations of dcc namely
> read, write, read/modify/write and loop. The probe method
> here instantiates all the resources necessary for dcc to
> operate mainly the dedicated dcc sram where it stores the
> values. The DCC driver can be used for debugging purposes
> without going for a reboot since it can perform software
> triggers as well based on user inputs.
> 
> Also add the documentation for debugfs entries which explains
> the functionalities of each debugfs file that has been created
> for dcc.
> 
> The following is the justification of using debugfs interface
> over the other alternatives like sysfs/ioctls
> 
> i) As can be seen from the debugfs attribute descriptions,
> some of the debugfs attribute files here contains multiple
> arguments which needs to be accepted from the user. This goes
> against the design style of sysfs.
> 
> ii) The user input patterns have been made simple and convenient
> in this case with the use of debugfs interface as user doesn't
> need to shuffle between different files to execute one instruction
> as was the case on using other alternatives.
> 

I would have preferred to get some more input from users of the debugfs
interface, but it's after all not ABI. So let's get this merged and
if people has concerns/objections/suggestions we'll improve it as
necessary.

Thanks for pushing this Souradeep!

> Signed-off-by: Souradeep Chowdhury <quic_schowdhu@...cinc.com>
> Reviewed-by: Alex Elder <elder@...aro.org>

Thanks Alex.

Regards,
Bjorn