linux-kernel - Re: [PATCH v1] media: si2168: Refactor command setup code

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Message-ID: <20190702095109.GC22408@latitude>
Date:   Tue, 2 Jul 2019 11:51:09 +0200
From:   Jonathan Neuschäfer <j.neuschaefer@....net>
To:     Marc Gonzalez <marc.w.gonzalez@...e.fr>
Cc:     Antti Palosaari <crope@....fi>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media <linux-media@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Jonathan Neuschäfer <j.neuschaefer@....net>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Brad Love <brad@...tdimension.cc>
Subject: Re: [PATCH v1] media: si2168: Refactor command setup code

Hi,

On Mon, Jul 01, 2019 at 01:44:09PM +0200, Marc Gonzalez wrote:
> By refactoring the command setup code, we can let the compiler
> determine the size of each command.

I like the idea, it definitely saves some code.

The conversion also looks correct.

> Signed-off-by: Marc Gonzalez <marc.w.gonzalez@...e.fr>
> ---
>  drivers/media/dvb-frontends/si2168.c | 142 ++++++++-------------------
>  1 file changed, 41 insertions(+), 101 deletions(-)
> 
> diff --git a/drivers/media/dvb-frontends/si2168.c b/drivers/media/dvb-frontends/si2168.c
> index 168c503e9154..19398f041c79 100644
> --- a/drivers/media/dvb-frontends/si2168.c
> +++ b/drivers/media/dvb-frontends/si2168.c
> @@ -11,6 +11,12 @@
>  
>  static const struct dvb_frontend_ops si2168_ops;
>  
> +#define CMD_SETUP(cmd, __args, __rlen) do {	\
> +	int wlen = sizeof(__args) - 1;		\
> +	memcpy(cmd.args, __args, wlen);		\
> +	cmd.wlen = wlen; cmd.rlen = __rlen;	\
> +} while (0)

It would be nice for casual readers to have a little comment here, that
explains (briefly) what this macro does, and what the arguments mean,
and their types.

Why cmd rather than __cmd? This seems inconsistent.

The wlen local variable can be avoided by a bit of suffling:

	#define CMD_SETUP(cmd, __args, __rlen) do {	\
		cmd.rlen = __rlen;			\
		cmd.wlen = sizeof(__args) - 1;		\
		memcpy(cmd.args, __args, cmd.wlen);	\
	} while (0)


[from the other mail]
> I'm planning on sending a v2 where drivers/media/tuners/si2157.c
> is refactored the same way.

Makes sense.

> Not sure where to store the macro. Maybe include/media/dvb_frontend.h?

Then include/media/dvb_frontend.h would contain information about the
private structs of a few (two) drivers. This doesn't seem like a good
idea to me.


Greetings,
Jonathan Neuschäfer

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