linux-kernel - Re: [PATCH v10 2/4] media: i2c: Add MAX9286 driver

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Message-ID: <20200723222834.GC829@valkosipuli.retiisi.org.uk>
Date:   Fri, 24 Jul 2020 01:28:34 +0300
From:   Sakari Ailus <sakari.ailus@....fi>
To:     Kieran Bingham <kieran.bingham@...asonboard.com>
Cc:     Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        linux-renesas-soc@...r.kernel.org, linux-media@...r.kernel.org,
        linux-gpio@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Jacopo Mondi <jacopo@...ndi.org>,
        Niklas Söderlund 
        <niklas.soderlund@...natech.se>, Hans Verkuil <hverkuil@...all.nl>,
        Hyun Kwon <hyunk@...inx.com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
        Niklas Söderlund 
        <niklas.soderlund+renesas@...natech.se>
Subject: Re: [PATCH v10 2/4] media: i2c: Add MAX9286 driver

Hi Kieran,

On Thu, Jul 16, 2020 at 10:02:24AM +0100, Kieran Bingham wrote:
> Hi Sakari,
> 
> This is the output of checkpatch --strict on this driver. Sorry for not
> detailing this in the commit or cover letter.

No worries.

> 
> > ./patches/gmsl/v10/v10-0001-dt-bindings-media-i2c-Add-bindings-for-Maxim-Int.patch has style problems, please review.
> > --------------------------------------------------------------
> > ./patches/gmsl/v10/v10-0002-media-i2c-Add-MAX9286-driver.patch
> > --------------------------------------------------------------
> > CHECK: Prefer using the BIT macro
> > #246: FILE: drivers/media/i2c/max9286.c:40:
> > +#define MAX9286_FSYNCMODE_INT_OUT	(1 << 6)
> > 
> > CHECK: Prefer using the BIT macro
> > #251: FILE: drivers/media/i2c/max9286.c:45:
> > +#define MAX9286_FSYNCMETH_SEMI_AUTO	(1 << 0)
> > 
> > CHECK: Prefer using the BIT macro
> > #262: FILE: drivers/media/i2c/max9286.c:56:
> > +#define MAX9286_EDC_6BIT_CRC		(1 << 5)
> > 
> > CHECK: Prefer using the BIT macro
> > #268: FILE: drivers/media/i2c/max9286.c:62:
> > +#define MAX9286_HVSRC_D14		(1 << 0)
> > 
> > CHECK: Prefer using the BIT macro
> > #286: FILE: drivers/media/i2c/max9286.c:80:
> > +#define MAX9286_DATATYPE_RGB565		(1 << 0)
> > 
> > CHECK: Prefer using the BIT macro
> > #304: FILE: drivers/media/i2c/max9286.c:98:
> > +#define MAX9286_I2CSLVSH_469NS_234NS	(1 << 5)
> > 
> > CHECK: Prefer using the BIT macro
> > #312: FILE: drivers/media/i2c/max9286.c:106:
> > +#define MAX9286_I2CMSTBT_28KBPS		(1 << 2)
> > 
> > CHECK: Prefer using the BIT macro
> > #316: FILE: drivers/media/i2c/max9286.c:110:
> > +#define MAX9286_I2CSLVTO_256US		(1 << 0)
> 
> None of those are appropriate to use the BIT() macro, as they are all
> entries of a specific field with a shift, such as:
> 
> #define MAX9286_FSYNCMODE_ECU           (3 << 6)
> #define MAX9286_FSYNCMODE_EXT           (2 << 6)
> #define MAX9286_FSYNCMODE_INT_OUT       (1 << 6)
> #define MAX9286_FSYNCMODE_INT_HIZ       (0 << 6)
> 
> Checkpatch is only picking up on the "1 << x" variant of each entry.

Ideally you should use "1U << x" everywhere. If you happen to have a
register with 31st bit signifying something, mayhem would follow. So the
practice is to make all such definitions unsigned.

> 
> 
> > CHECK: Macro argument reuse 'source' - possible side-effects?
> > #399: FILE: drivers/media/i2c/max9286.c:193:
> > +#define for_each_source(priv, source) \
> > +	for ((source) = NULL; ((source) = next_source((priv), (source))); )
> 
> This warns against possible side effects, but the 're-use' effects are
> desired ;-)
> 
> If you'd prefer this macro to be re-written please let me know.

Works for me. Some warnigns are just not useful. I bet quite a few macros
elsewhere in the kernel would trigger this.

> 
> 
> > CHECK: Lines should not end with a '('
> > #1372: FILE: drivers/media/i2c/max9286.c:1166:
> > +			ret = v4l2_fwnode_endpoint_parse(
> 
> Full code block:
> 
> >                         ret = v4l2_fwnode_endpoint_parse(
> >                                         of_fwnode_handle(node), &vep);
> >                         if (ret) {
> >                                 of_node_put(node);
> >                                 return ret;
> >                         }
> 
> That one is awkward, and I chose to keep it as a lesser evil.
> Of course now that we can officially go up to 120 chars, I could move
> this line up.
> 
> If you'd like this to be moved to a single line now we can go over 80
> chars, please confirm.

I don't mind that. Mauro, any thoughts on this?

-- 
Kind regards,

Sakari Ailus