On Friday 18 May 2012 07:09 PM, Tomi Valkeinen wrote:
Hi,
On Tue, 2012-05-15 at 11:32 +0530, Archit Taneja wrote:
DSI supports interleaving of command mode packets during the HSA, HFP, HBP and
BLLP blanking intervals in a video mode stream. This is useful as a user may
want to read or change the configuration of a panel without stopping the video
stream.
On OMAP DSI, we can queue HS or LP command mode packets in the TX FIFO, and
the DSI HW takes care of interleaving this data during the one of the blanking
intervals. The DSI HW needs to be programmed with the maximum amount of data
that can be interleaved in a particular blanking period. A blanking period
cannot be used to send command mode data for it's complete duration, there is
some amount of time required for the DSI data and clock lanes to transition
to the desired LP or HS state.
Based on the state of the lanes at the beginning and end of the blanking period,
we have different scenarios, with each scenario having a different value of time
required to transition to HS or LP. Refer to the section 'Interleaving Mode' in
OMAP TRM for more info on the scenarios and the equations to calculate the time
required for HS or LP transitions.
We use the scenarios which takes the maximum time for HS or LP transition, this
gives us the minimum amount of time that can be used to interleave command mode
data. The amount of data that can be sent during this minimum time is calculated
for command mode packets both in LP and HS. These are written to the registers
DSI_VM_TIMING4 to DSI_VM_TIMING6.
The calculations don't take into account the time required of transmitting BTA
when doing a DSI read, or verifying if a DSI write went through correctly. Until
these latencies aren't considered, the behaviour of DSI is unpredictable when
a BTA is interleaved during a blanking period. Enhancement of these calculations
is a TODO item.
The code in dsi_config_cmd_mode_interleaving() looks a bit long and
confusing, but I don't think it's trivial to simplify it. There's just
so many variables to consider.
There is a little optimisation done in the code to not calculate the
interleaving parameter for a blanking period which is not used for
interleaving. Checks like below are done for that:
if(!hsa_blanking_mode) {
...
}
if (!hfp_blanking_mode) {
...
}
...
We could remove this, as the computation is just done once and there
seems to be no side effects to write interleaving parameters for a
blanking period not used for interleaving. But it won't make much
function much simpler.
In the future I think we should store the DSI configurations into
memory, so that we don't need to parse the hardware registers to find
out things like DSI timings.
Yes, I'll do this clean up sometime soon.
Archit
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