linux-kernel - Re: [PATCH v1] HID: i2c-hid: use print_hex_dump

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Date:   Tue, 15 Aug 2023 14:58:41 +0800
From:   Riwen Lu <luriwen@...mail.com>
To:     Rahul Rameshbabu <sergeantsagara@...tonmail.com>
Cc:     Jiri Kosina <jikos@...nel.org>, benjamin.tissoires@...hat.com,
        dmitry.torokhov@...il.com, linux@...ssschuh.net,
        hdegoede@...hat.com, rrangel@...omium.org,
        u.kleine-koenig@...gutronix.de, linux-input@...r.kernel.org,
        linux-kernel@...r.kernel.org, Riwen Lu <luriwen@...inos.cn>
Subject: Re: [PATCH v1] HID: i2c-hid: use print_hex_dump_debug to print report
 descriptor

在 2023/8/15 14:35, Rahul Rameshbabu 写道:
> 
> On Tue, 15 Aug, 2023 14:02:40 +0800 "Riwen Lu" <luriwen@...mail.com> wrote:
>> 在 2023/8/14 17:26, Jiri Kosina 写道:
>>> On Mon, 3 Jul 2023, Riwen Lu wrote:
>>>
>>>> From: Riwen Lu <luriwen@...inos.cn>
>>>>
>>>> The format '%*ph' print up to 64 bytes long as a hex string with ' '
>>>> sepatator. Usually the size of report descriptor is larger than 64
>>>> bytes, so consider using print_hex_dump_debug to print out all of it for
>>>> better debugging.
>>>>
>>>> Signed-off-by: Riwen Lu <luriwen@...inos.cn>
>>>> ---
>>>>    drivers/hid/i2c-hid/i2c-hid-core.c | 4 +++-
>>>>    1 file changed, 3 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/hid/i2c-hid/i2c-hid-core.c b/drivers/hid/i2c-hid/i2c-hid-core.c
>>>> index efbba0465eef..8e97fc01c852 100644
>>>> --- a/drivers/hid/i2c-hid/i2c-hid-core.c
>>>> +++ b/drivers/hid/i2c-hid/i2c-hid-core.c
>>>> @@ -772,7 +772,9 @@ static int i2c_hid_parse(struct hid_device *hid)
>>>>    		}
>>>>    	}
>>>>
>>>> -	i2c_hid_dbg(ihid, "Report Descriptor: %*ph\n", rsize, rdesc);
>>>> +	i2c_hid_dbg(ihid, "Report Descriptor\n");
>>>> +	print_hex_dump_debug("  ", DUMP_PREFIX_OFFSET, 16, 1,
>>>> +			rdesc, rsize, false);
> 
> Maybe it makes sense to use a prefix for the hex dump that is easy to
> trace rather than padding whitespace? This looks good when you do not
> see any other kernel message log lines get interlaced when written.
> However, if you have a lot of concurrent kernel message output, I think
> it can be tough to piece together the lines of the dump with this
> prefix. Just my opinion.
> 
That's a good opinion. I'll make a v2 version.

Thanks.
>>>
>>> But that would dump it unconditionally, while i2c_hid_dbg() is
>>> conditional.
>>>
>> Function print_hex_dump_debug() dump messages is as conditional as
>> i2c_hid_dbg().
>>
>> The function i2c_hid_dbg() defines as follows:
>> #define i2c_hid_dbg(ihid, ...) dev_dbg(&(ihid)->client->dev, __VA_ARGS__)
>>
>> dev_dbg() depends on the same macro as print_hex_dump_debug().
> 
> I agree with this point. Both dev_dbg and print_hex_dump_debug are noops
> if neither CONFIG_DYNAMIC_DEBUG is set or DEBUG is defined.
> 
> --
> Thanks,
> 
> Rahul Rameshbabu
>