Re: [PATCH 10/10] OMAP: DSS2: DSI Video mode support

[Archit Taneja <archit@ti.com>]

On Friday 02 September 2011 01:25 PM, Valkeinen, Tomi wrote:
> On Fri, 2011-09-02 at 11:43 +0530, Archit Taneja wrote:
>>> Sending a null packet to start the DDR clk is rather OMAP specific
>>> internal thing, so I don't want to require the panel driver to need
>> to
>>> know that it must send a null packet to start the clock. So if the
>> ddr
>>> clk is not started automatically, I think we should have a function
>> to
>>> do that (dsi_start_ddr_clk or whatever), which will then send the
>> null
>>> packet (and perhaps return an error if DDR_CLK_ALWAYS_ON is not set,
>>> dunno...).
>>
>> Okay, If we can confirm that a panel asks for DDR_CLK_ALWAYS_ON
>> mainly
>> because it doesn't have its own fclk, then the dsi driver surely
>> needs
>> to start the DDR clock by sending a NULL packet.
>>
>> If this is to be done, one thing that has to be thought of is:
>>
>> - We need one of the requested VC's to be in HS mode for this. Do we
>> enable HS for a VC in the dsi driver itself? Currently, its the job
>> of
>> the panel driver to enable HSmode for a VC. Is this a clean approach?
>
> I have to say I don't have any idea what would be the best approach...
>
> What comes to my mind is that the DSI driver could automatically send
> the null packet, when:
>
> a) ddr_clk_always_on is set
> b) a channel is changed to HS and enabled (I guess it needs to be
> enabled also, does it?)

This approach sounds fine. The only drawback is that we send a NULL 
packet each time we enable a high speed channel. So if a panel is using 
2 VCs, and it wants high speed for both channels(for some reason), we 
will be sending a NULL packet unnecessarily.

One observation was that the DDR clock has to be enabled only after the 
bridge chip is reset. Enabling HS, and sending a NULL packet before 
doing a hw reset of the bridge chip doesn't bring up the panel(that is a 
bit peculiar). So we can't do this within omapdss_dsi_display_enable().

Archit

>
> Well, we do seem to enable all VCs at init phase (which, thinking about
> it, sounds a bit odd), so in practice we would just need to handle the
> omapdss_dsi_vc_enable_hs() case.
>
>   Tomi
>
>