Linux-Media Archive on lore.kernel.org
 help / color / Atom feed
From: Hans Verkuil <hverkuil@xs4all.nl>
To: Matt Ranostay <matt.ranostay@konsulko.com>
Cc: linux-media@vger.kernel.org
Subject: Re: [PATCH] media: video-i2c: add mlx90640 subpage data to output
Date: Fri, 16 Aug 2019 09:57:06 +0200
Message-ID: <1e1c0962-5b13-3d49-f946-a7a5896e8489@xs4all.nl> (raw)
In-Reply-To: <CAJCx=g=XOU72ZETpOHCdFfhC-9vkxAk09nTjaap4yGKB9+RKBA@mail.gmail.com>

On 8/15/19 8:23 AM, Matt Ranostay wrote:
> On Mon, Aug 12, 2019 at 6:05 AM Hans Verkuil <hverkuil@xs4all.nl> wrote:
>>
>> Hi Matt,
>>
>> On 8/11/19 9:10 AM, Matt Ranostay wrote:
>>> Add current subpage data via the status register to the video
>>> frame in the last word of data, which seems to be unused
>>> undocumented reserved data.
>>
>> I don't really understand from this description what is going on
>> here.
> 
> Probably can make it more verbose if requested.
> 
> But simple overview is that all the frame data is from 0x400 read but
> there is a some status register data that is from 0x8000
> that needs to be read.
> 
> So mostly from the latter read (which can have an unlikely race
> condition and be incorrect) is to confirm which sub frame that is
> being read which can be one or two. You need the previous subpage
> magic values to process that respective frame temperature data.

But 1) you are overwriting the last pixel value of the frame with this
status value and 2) it is undocumented so how would applications handle
this?

As far as I can tell you are just replacing the last 'pixel' in the
buffer with a magic value without explaining what it is or what userspace
should do with it. And exposing low-level register information to userspace
is almost always wrong.

So: what is this status value? How should it be used?

Regards,

	Hans

> 
>>
>> mlx90640_xfer() reads the buffer data from the i2c device, but
>> that data is split over two different addresses? Or does
>> 0x8000 contain something else with a different meaning compared
>> to what is read from 0x400?
>>
>>>
>>> Signed-off-by: Matt Ranostay <matt.ranostay@konsulko.com>
>>> ---
>>>  drivers/media/i2c/video-i2c.c | 12 ++++++++++--
>>>  1 file changed, 10 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/media/i2c/video-i2c.c b/drivers/media/i2c/video-i2c.c
>>> index 078141712c88..8bc7b228ba40 100644
>>> --- a/drivers/media/i2c/video-i2c.c
>>> +++ b/drivers/media/i2c/video-i2c.c
>>> @@ -168,8 +168,16 @@ static int amg88xx_xfer(struct video_i2c_data *data, char *buf)
>>>
>>>  static int mlx90640_xfer(struct video_i2c_data *data, char *buf)
>>>  {
>>> -     return regmap_bulk_read(data->regmap, 0x400, buf,
>>> -                             data->chip->buffer_size);
>>> +     int ret = regmap_bulk_read(data->regmap, 0x400, buf,
>>> +                                data->chip->buffer_size);
>>
>> Shouldn't this be data->chip->buffer_size - size, since the last
>> 'size' bytes will be overwritten anyway?
> 
> Yes that is true but don't see in datasheet that you can just not read
> the last two bytes of the transaction.
> Probably totally fine to not do so but who knows.
> 
> - Matt
> 
>>
>>> +     int size = data->chip->bpp / 8;
>>> +
>>> +     if (ret)
>>> +             return ret;
>>> +
>>> +     /* read status register, which contains subpage that is read */
>>> +     return regmap_bulk_read(data->regmap, 0x8000,
>>> +                             &buf[data->chip->buffer_size - size], size);
>>>  }
>>>
>>>  static int amg88xx_setup(struct video_i2c_data *data)
>>>
>>
>> Regards,
>>
>>         Hans


      reply index

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-11  7:10 Matt Ranostay
2019-08-12 13:05 ` Hans Verkuil
2019-08-15  6:23   ` Matt Ranostay
2019-08-16  7:57     ` Hans Verkuil [this message]

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=1e1c0962-5b13-3d49-f946-a7a5896e8489@xs4all.nl \
    --to=hverkuil@xs4all.nl \
    --cc=linux-media@vger.kernel.org \
    --cc=matt.ranostay@konsulko.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-Media Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-media/0 linux-media/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-media linux-media/ https://lore.kernel.org/linux-media \
		linux-media@vger.kernel.org linux-media@archiver.kernel.org
	public-inbox-index linux-media


Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-media


AGPL code for this site: git clone https://public-inbox.org/ public-inbox