Re: [PATCH v2 0/3] media: vimc: Allow multiple capture devices to use the same sensor

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Kaaira,

Thank you for the patches.

On Fri, Jul 24, 2020 at 05:32:10PM +0530, Kaaira Gupta wrote:
> This is version 2 of the patch series posted by Niklas for allowing
> multiple streams in VIMC.
> The original series can be found here:
> https://patchwork.kernel.org/cover/10948831/
> 
> This series adds support for two (or more) capture devices to be 
> connected to the same sensors and run simultaneously. Each capture device 
> can be started and stopped independent of each other.
> 
> Patch 1/3 and 2/3 deals with solving the issues that arises once two 
> capture devices can be part of the same pipeline. While 3/3 allows for 
> two capture devices to be part of the same pipeline and thus allows for 
> simultaneously use.

I think this is really nice work, as it will make the vimc driver even
more useful for testing purposes.

I however just noticed that the patches seem to have lost Niklas'
authorship. Niklas posted v1 ([1]), and while there's absolutely no
issue with taking over a patch series (especially when the original
author is aware of that, and approves :-)), it's customary to keep the
original authorship.

Authorship, as recorded in the commit's "Author:" field (displayed by
"git show" or "git log" for instance), is distinct from Signed-off-by.
The original Signed-off-by line needs to be preserved to indicate the
original author's commitment to the certificate of origin ([2]), but in
itself that doesn't acknowledge original authorship of the code.

I'm sure this is an oversight. Authorship can easily be changed with the
--author option to "git commit --amend".

$ git show -s
commit 8be3a53e18e0e1a98f288f6c7f5e9da3adbe9c49 (HEAD -> tmp)
Merge: fc10807db5ce 3c597282887f
Author: Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed Jun 24 17:39:30 2020 -0700

    Merge tag 'erofs-for-5.8-rc3-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs

    Pull erofs fix from Gao Xiang:
     "Fix a regression which uses potential uninitialized high 32-bit value
      unexpectedly recently observed with specific compiler options"

    * tag 'erofs-for-5.8-rc3-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs:
      erofs: fix partially uninitialized misuse in z_erofs_onlinepage_fixup
$ git commit --amend --author 'Laurent Pinchart <laurent.pinchart@ideasonboard.com>'
[tmp 6a7191c2aee9] Merge tag 'erofs-for-5.8-rc3-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs
 Date: Wed Jun 24 17:39:30 2020 -0700
$ git show -s
commit 6a7191c2aee9e4a2ba375f14c821bc9b4d7f881b (HEAD -> tmp)
Merge: fc10807db5ce 3c597282887f
Author: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Date:   Wed Jun 24 17:39:30 2020 -0700

    Merge tag 'erofs-for-5.8-rc3-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs
    
    Pull erofs fix from Gao Xiang:
     "Fix a regression which uses potential uninitialized high 32-bit value
      unexpectedly recently observed with specific compiler options"
    
    * tag 'erofs-for-5.8-rc3-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs:
      erofs: fix partially uninitialized misuse in z_erofs_onlinepage_fixup

Not that I would try to take ownership of a commit authored by Linus, I
doubt he would appreciate that :-)

Authorship is normally preserved through git-format-patch,
git-send-email and git-am:

- git-format-patch sets the "From:" line to the patch's author

- If the "From:" line is different than the mail sender, git-send-email
  replaces it with the sender's identity (as we don't want to forge
  e-mails with an incorrect sender). It then adds the original "From:"
  line *inside* the mail, just after the headers, right before the body
  of the commit message.

- git-am sets the author to the "From:" line from the e-mail's body if
  it exists, and uses the "From:" line from the e-mail's header (the
  sender's identity) otherwise.

If you use those tools authorship should get preserved automatically.

Of course new patches that you would add to the series should have your
authorship.

I hope this helps clarifying the process, please let me know if you have
any question.

[1] https://lore.kernel.org/linux-media/20190518010744.15195-1-niklas.soderlund+renesas@ragnatech.se/
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst#n431

> Changes since v1:
> 	- All three patches rebased on latest media-tree.
> 	Patch 3:
> 	- Search for an entity with a non-NULL pipe instead of searching
> 	  for sensor. This terminates the search at output itself.
> 
> Kaaira Gupta (3):
>   media: vimc: Add usage count to subdevices
>   media: vimc: Serialize vimc_streamer_s_stream()
>   media: vimc: Join pipeline if one already exists
> 
>  .../media/test-drivers/vimc/vimc-capture.c    | 35 ++++++++++++++++++-
>  .../media/test-drivers/vimc/vimc-debayer.c    |  8 +++++
>  drivers/media/test-drivers/vimc/vimc-scaler.c |  8 +++++
>  drivers/media/test-drivers/vimc/vimc-sensor.c |  9 ++++-
>  .../media/test-drivers/vimc/vimc-streamer.c   | 23 +++++++-----
>  5 files changed, 73 insertions(+), 10 deletions(-)

-- 
Regards,

Laurent Pinchart