Re: [PATCH] OMAP: DSS2: DSI: Support non-dcs long read

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2011/8/5 Tomi Valkeinen <tomi.valkeinen@xxxxxx>:
> Hi,
>
> On Fri, 2011-08-05 at 00:17 -0700, Arve Hjønnevåg wrote:
>> 2011/8/5 Tomi Valkeinen <tomi.valkeinen@xxxxxx>:
>> > On Thu, 2011-08-04 at 18:15 -0700, Arve Hjønnevåg wrote:
>> >> 2011/8/4 Tomi Valkeinen <tomi.valkeinen@xxxxxx>:
>> >> > Hi,
>> >> >
>> >> > On Wed, 2011-06-29 at 20:44 -0700, Arve Hjønnevåg wrote:
>> >> >> Change-Id: I18168c887e1384c07dc033a1ffc57abdacb26073
>> >> >> Signed-off-by: Arve Hjønnevåg <arve@xxxxxxxxxxx>
>> >> >> ---
>> >> >>  drivers/video/omap2/dss/dsi.c |    7 ++++++-
>> >> >>  1 files changed, 6 insertions(+), 1 deletions(-)
>> >> >
>> >> > This feels somehow partial... Why do you want to read generic packets if
>> >> > there are no functions to send generic packets?
>> >> >
>> >>
>> >> The chip responds with a generic packet when reading from some
>> >> registers. This is a simple fix while adding support for sending
>> >> generic packets would probably require an api change.
>> >
>> > What command do you use to read the register? DCS? If so, sounds rather
>> > strange HW implementation.
>> >
>>
>> This change modifies dsi_vc_dcs_read to accept a generic response
>
> Ok, so you do send a DCS read command, and you get a generic response.
>
>> packet. If you want a separate generic read command that would also
>> work, but the it would make it a little harder to write the driver
>> since you then would need to know what type of response the chip
>> sends.
>
> Well, you do know what type of response the chip sends. According to

Only because the dsi_vc_dcs_read failed. The examples in the datasheet
only show dcs commands and responses.

> MIPI DSI spec, a DCS read is answered with DCS short/long response, and
> a generic read is answered with generic short/long response.
>

I don't have that spec, but if the command type dictates the response
type, then I agree that having separate a generic_read command is
better.

> If your HW doesn't work like that, it's against the spec. If a broken
> chip like that was widely used, I guess we would have to add a hack for
> that, but until such day I want to keep the driver working as the spec
> says.
>

My guess is that it would also respond to a generic read, but I have
not tried this since I did not know there were multiple read commands.

-- 
Arve Hjønnevåg
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