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

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Date:   Wed, 3 Jul 2019 16:15:35 +0200
From:   Marc Gonzalez <marc.w.gonzalez@...e.fr>
To:     Jonathan Neuschäfer <j.neuschaefer@....net>,
        Antti Palosaari <crope@....fi>,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     linux-media <linux-media@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Brad Love <brad@...tdimension.cc>
Subject: Re: [PATCH v1] media: si2168: Refactor command setup code

On 03/07/2019 14:47, Marc Gonzalez wrote:

> Come to think of it, I'm really not a fan of "large" macro functions.
> I'll outline a different option in v2.

My idea is to use a trivial helper function to assign the 3 struct fields,
and then a trivial macro to invoke the helper:

static void cmd_setup(struct si2168_cmd *cmd, char *args, int wlen, int rlen)
{
	memcpy(cmd->args, args, wlen);
	cmd->wlen = wlen;
	cmd->rlen = rlen;
}

#define CMD_SETUP(cmd, args, rlen) \
	cmd_setup(cmd, args, sizeof(args) - 1, rlen)

I think this way addresses all of your comments:

- since we're using a real function, the compiler can perform type-checking,
and the function's prototype is self-documenting.
- no more funky __args and __rlen arguments
- no local variables

Note however, that drivers/media/tuners/si2157.c uses a different struct
(struct si2157_cmd). Therefore, if we wanted to apply the same changes
to si2157.c, we would have to define a common struct, and replace all
the uses of struct si2157_cmd and struct si2168_cmd. That seemed too
invasive to do without the maintainer's approval and guidance.

Antti, do you Ack this new approach?

It's not clear what HW is supported by drivers/media/dvb-frontends/si21xx.c
(that's a very generic name).

Regards.