linux-kernel - Re: [PATCH v5 03/16] media: rkisp1: Add user space ABI definitions

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Date:   Thu, 8 Mar 2018 18:00:45 +0800
From:   Jacob Chen <jacobchen110@...il.com>
To:     Hans Verkuil <hverkuil@...all.nl>
Cc:     Shunqian Zheng <zhengsq@...k-chips.com>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Tomasz Figa <tfiga@...omium.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        钟以崇 <zyc@...k-chips.com>,
        Eddie Cai <eddie.cai.linux@...il.com>,
        Jeffy Chen <jeffy.chen@...k-chips.com>,
        Allon Huang <allon.huang@...k-chips.com>,
        devicetree@...r.kernel.org, Heiko Stuebner <heiko@...ech.de>,
        robh+dt@...nel.org, Joao Pinto <Joao.Pinto@...opsys.com>,
        Luis Oliveira <Luis.Oliveira@...opsys.com>,
        Jose Abreu <Jose.Abreu@...opsys.com>
Subject: Re: [PATCH v5 03/16] media: rkisp1: Add user space ABI definitions

Hi Hans,

2018-02-07 20:00 GMT+08:00 Hans Verkuil <hverkuil@...all.nl>:
> On 12/29/17 08:52, Shunqian Zheng wrote:
>> From: Jeffy Chen <jeffy.chen@...k-chips.com>
>>
>> Add the header for userspace
>
> General note: I saw four cases where this documentation referred to the
> datasheet. Three comments on that:
>
> 1) You don't say which datasheet.
> 2) I assume the datasheet is under NDA?

This datasheet can't be got by customers, even under NDA.

> 3) You do need to give enough information so a reasonable default can be
>    used. I mentioned in an earlier review that creating an initial params
>    struct that can be used as a templete would be helpful (or even
>    required), and that would be a good place to put such defaults.
>

It don't need a default config
For applcation writers, they can just init it with zero data, and only
set value for the part they concerned.

As for ABI, i have checked there is no mismatches.
Those structures is 32 bit aligned both in 64bit/32bit env, since
there is no 64bit value.
"__attribute__ ((packed))" can avoid mismatches happen when we add a
64bit value to those structures.

As robin said, enums and bools are not guaranteed to be consistent
between different compiler, so it's a potential risk.
I have replace bools with unsigned char and enums with unsigned int.


> Regards,
>
>         Hans