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Reply-To: kieran.bingham@ideasonboard.com
Subject: Re: [PATCH v10 2/4] media: i2c: Add MAX9286 driver
To:     Sakari Ailus <sakari.ailus@iki.fi>
Cc:     Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>,
        linux-renesas-soc@vger.kernel.org, linux-media@vger.kernel.org,
        linux-gpio@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Jacopo Mondi <jacopo@jmondi.org>,
        =?UTF-8?Q?Niklas_S=c3=b6derlund?= <niklas.soderlund@ragnatech.se>,
        Hans Verkuil <hverkuil@xs4all.nl>,
        Hyun Kwon <hyunk@xilinx.com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        Jacopo Mondi <jacopo+renesas@jmondi.org>,
        Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>,
        =?UTF-8?Q?Niklas_S=c3=b6derlund?= 
        <niklas.soderlund+renesas@ragnatech.se>
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From:   Kieran Bingham <kieran.bingham@ideasonboard.com>
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Organization: Ideas on Board
Message-ID: <c4b0e30f-b0b7-1b19-f43e-36d417eb6d28@ideasonboard.com>
Date:   Fri, 24 Jul 2020 10:32:11 +0100
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Hi Sakari,

On 23/07/2020 23:28, Sakari Ailus wrote:
> 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.

Just to clarify, because of the location you've put your x, which is not
the variable in the above case.

These definitions are possible field values with a shift (enum << y),
not bit values (1 << x)

They can of course be unsigned though.

Is your statement that you would like to see these as:

 #define MAX9286_FSYNCMODE_ECU           (3U << 6)
 #define MAX9286_FSYNCMODE_EXT           (2U << 6)
 #define MAX9286_FSYNCMODE_INT_OUT       (1U << 6)
 #define MAX9286_FSYNCMODE_INT_HIZ       (0U << 6)


Or that you would prefer a macro'ised version:

#define FIELD_ENTRY(value, shift) (value U << shift)


Or rather, I could just convert them all to use FIELD_PREP:

#define MAX9286_FSYNCMODE GENMASK(7,6)

#define MAX9286_FSYNCMODE_ECU      FIELD_PREP(MAX9286_FSYNCMODE, 3)
#define MAX9286_FSYNCMODE_EXT      FIELD_PREP(MAX9286_FSYNCMODE, 2)
#define MAX9286_FSYNCMODE_INT_OUT  FIELD_PREP(MAX9286_FSYNCMODE, 1)
#define MAX9286_FSYNCMODE_INT_HIZ  FIELD_PREP(MAX9286_FSYNCMODE, 0)

If you want me to change these entries, I suspect moving wholly to use
FIELD_PREP/FIELD_GET throughout the driver would be the best course of
action.

A bit of churn, but I can do that if you wish.

--
Kieran


>>> 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.


I think we'll just leave this one ;-)


>>> 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?


And I'll let Mauro decide that as it will impact my line-length choices
in the future ;-)


-- 
Regards
--
Kieran