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Subject: Re: [PATCH 0/2] Use Media Dev Allocator to fix vimc dev lifetime bugs
To:     Hans Verkuil <hverkuil-cisco@xs4all.nl>
Cc:     Shuah Khan <skhan@linuxfoundation.org>,
        linux-media@vger.kernel.org, linux-kernel@vger.kernel.org
References: <cover.1558667245.git.skhan@linuxfoundation.org>
 <c9160fe7-e880-4070-3959-b9e9177acf54@xs4all.nl>
From:   Helen Koike <helen.koike@collabora.com>
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Date:   Thu, 13 Jun 2019 10:24:28 -0300
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On 6/13/19 2:44 AM, Hans Verkuil wrote:
> On 5/24/19 5:31 AM, Shuah Khan wrote:
>> media_device is embedded in struct vimc_device and when vimc is removed
>> vimc_device and the embedded media_device goes with it, while the active
>> stream and vimc_capture continue to access it.
>>
>> Fix the media_device lifetime problem by changing vimc to create shared
>> media_device using Media Device Allocator API and vimc_capture getting
>> a reference to vimc module. With this change, vimc module can be removed
>> only when the references are gone. vimc can be removed after vimc_capture
>> is removed.
>>
>> Media Device Allocator API supports just USB devices. Enhance it
>> adding a genetic device allocate interface to support other media
>> drivers.
>>
>> The new interface takes pointer to struct device instead and creates
>> media device. This interface allows a group of drivers that have a
>> common root device to share media device resource and ensure media
>> device doesn't get deleted as long as one of the drivers holds its
>> reference.
>>
>> The new interface has been tested with vimc component driver to fix
>> panics when vimc module is removed while streaming is in progress.
> 
> Helen, can you review this series? I'm not sure this is the right approach
> for a driver like vimc, and even if it is, then it is odd that vimc-capture
> is the only vimc module that's handled here.

Hi Hans,

Yes, I can take a look. Sorry, I've been a bit busy these days but I'll
try to take a look at this patch series (and the others) asap.

Helen

> 
> My gut feeling is that this should be handled inside vimc directly and not
> using the media-dev-allocator.
> 
> Regards,
> 
> 	Hans
> 
>>
>> Shuah Khan (2):
>>   media: add generic device allocate interface to media-dev-allocator
>>   vimc: fix BUG: unable to handle kernel NULL pointer dereference
>>
>>  drivers/media/Makefile                     |  4 +-
>>  drivers/media/media-dev-allocator.c        | 39 ++++++++++++++
>>  drivers/media/platform/vimc/vimc-capture.c | 17 +++++-
>>  drivers/media/platform/vimc/vimc-core.c    | 60 ++++++++++++----------
>>  include/media/media-dev-allocator.h        | 46 ++++++++++++++---
>>  5 files changed, 130 insertions(+), 36 deletions(-)
>>
>