On 23.11.2012 10:38, Thierry Reding wrote:
On Fri, Nov 23, 2012 at 10:24:22AM +0100, Christian König wrote:
Hi Thierry,
On 21.11.2012 16:01, Thierry Reding wrote:
This small series is very much work in progress, but I still wanted to
get feedback in this early stage to gather requirements from the folks
working on the display drivers that these helpers target.
Patch 1 in the series adds a generic helper to pack a structure that
describes an HDMI AVI infoframe into the binary format as specified in
the HDMI specification. The resulting binary buffer should be easily
programmable into the HDMI controller.
Patch 2 provides a helper to fill an HDMI AVI infoframe with data from
a struct drm_display_mode.
This is all pretty rough right now, but I think some feedback would be
good at this point, to see if the design is at all sensible. I should
also mention that I haven't actually tested this on real hardware yet.
Furthermore I have plans to add something similar for the other types
of infoframes specified by HDMI once the direction becomes clearer.
In general I like the idea of storing the informations in a C struct
and only packing it into the binary form when needed.
I would rather like to see a complete implementation of all the
interesting HDMI packets, including the necessary
calculations/tables for audio timing recovery etc before it gets
committed upstream.
I'm afraid I'm not very familiar with those packets. Also I haven't seen
any actual users of audio timing recovery packets so far, so I'm not
sure that adding support for them would be very useful.
Take a look at: drivers/gpu/drm/radeon/r600_hdmi.c There we have
r600_hdmi_predefined_acr, r600_hdmi_calc_cts and r600_hdmi_acr doing the
audio clock recovery calculation/table manually. Those values are only
used as fallback, since the hardware can do the calculation on their own.
I'm not sure if anybody else is doing this calculation in any driver
code, but it definitely isn't driver specific and part of the HDMI
specification, so I would say that it belongs into the general purpose
file as well.
What I have added so far is support for audio and vendor-specific
infoframes, since those have actual users. I also noticed that i915
implements SPD infoframes as well, so I can extract that code into the
generic helpers as well.
Not sure about the separate configuration option. I'm not so much
into the config/build system of linux (I know that it is rather
complicated), but in general I would like to see that activated
automatically as soon as any driver starts using it (or at least the
driver depending on that option to be active).
The configuration option isn't supposed to be user visible. Drivers that
make use of this are supposed to select HDMI or DRM_HDMI to cause the
generic code to be pulled in.
Also two notes about the code in itself:
1. hdmi_avi_infoframe_pack: gets the size of the target buffer, but
unfortunately doesn't checks it.
That should already be fixed in the latest code in my local working
branch.
2. Separate the CRC calculation, we probably need that more than once.
I've also pulled that out into a separate function. I haven't made it a
public function yet, but I don't think that'll be necessary either since
it is used internally by the various infoframe packing functions.
Sounds good, let me know when you need a review of the code.
Christian.
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