RE: [PATCH] [media] s5p-mfc: add init buffer cmd to MFCV6

[Kamil Debski <k.debski@samsung.com>]

Hi Arun, 

> From: Arun Kumar K [mailto:arunkk.samsung@gmail.com]
> Sent: Friday, March 07, 2014 12:10 PM
> 
> Hi Sylwester,
> 
> On Fri, Mar 7, 2014 at 2:59 PM, Sylwester Nawrocki
> <s.nawrocki@samsung.com> wrote:
> > Hi,
> >
> > On 07/03/14 09:31, Arun Kumar K wrote:
> >> From: avnd kiran <avnd.kiran@samsung.com>
> >>
> >> Latest MFC v6 firmware requires tile mode and loop filter setting to
> >> be done as part of Init buffer command, in sync with v7. So, move
> >> these settings out of decode options reg.
> >> Also, make this register definition applicable from v6 onwards.
> >>
> >> Signed-off-by: avnd kiran <avnd.kiran@samsung.com>
> >> Signed-off-by: Arun Kumar K <arun.kk@samsung.com>
> >
> > Will the driver also work with older version of the firmware after
> > this change ? If not, shouldn't things like this be done depending on
> > what firmware version is loaded ?
> >
> 
> The original code was for the initial version of v6 firmware.
> After that the v6 firmware has got many fixes and updates which also
> got updated in the products running the same.
> As such there are no official multiple versions of v6 firmware, but
> only fixes / updates to older version. I will update the s5p-mfc-v6.fw
> in the linux-firmware also with the newer version. Hope that will be
> fine.

Unfortunately, I share the same concerns as Sylwester. We have two problems:
1) new kernel + old firmware

In this case, someone will update the kernel and find out that video
decoding is not working. An assumption that I think is common, is that
updating the kernel should not break anything. If it was working with the
previous version it should work with the next.

The solution I can suggest is that a check which firmware version is used
has to be implemented. Maybe you can use the date of firmware to do this
check?

2) old kernel + new firmware

I see no clear solution to this problem. If the kernel is old and the
firmware is behaving differently, the video decoding will not work. I can
guess that this case would be less common, but still a person can update the
firmware and leave the old kernel. Changing the firmware can be done by
replacing a single file.

In addition to the above, you need to clearly specify in the
linux-firmware.git what is going on. A readme file is a must. Maybe a second
v6 firmware file should be included?

Best wishes,
-- 
Kamil Debski
Samsung R&D Institute Poland