Re: [PATCH 4/4] drm/i915: Add support for Generic MIPI panel driver

Kumar, Shobhit
2014-05-22T07:45:24Z

On 5/21/2014 2:25 AM, Damien Lespiau wrote:
> On Tue, May 20, 2014 at 09:46:01PM +0530, Shobhit Kumar wrote:
>>> - UI is a period, so is homogeneous to time (s), but ui_num being in
>>> s^-1 and ui_den a constant, ui_num/ui_den looks like a frequency. Or
>>> could it be that UI = ui_den / ui_num? would be confusing, but the
>>> code below would make more sense. In which case could we have UI =
>>> ui_num / ui_den?
>>
>> I just kept ui_num and ui_den separately to take care of precision
>> loss, but I see how it is adding to confusion. Actually it is ui_den
>> / ui_num and we have all computations as 1/UI so it works. I think I
>> will compute UI directly as UI = (NS_KHZ_RATIO * 1000) /bitrate and
>> divide by 1000 wherever we use to maintain precision. Sounds ok ?
>
> I think just exchanging the two variable names (ui_num and ui_den)
> should be less work for you and should be enough. It's really just about
> having ui_num being the UI numerator so the reader is not too surprised

Yeah. Will fix this

>
>>>> + /* B044 */
>>>> + intel_dsi->hs_to_lp_count =
>>>> + CEIL_DIV(
>>>> + 4 * tlpx_ui + prepare_cnt * 2 +
>>>> + exit_zero_cnt * 2 + 10,
>>>> + 8);
>>>
>>> The previous was before I tried to look at the spec too closely. Mind
>>> explaining why we don't look at the HS to LP switch count? ie why HS to
>>> LP switch cound is always smaller than the LP to HS one?
>>
>> Because LP to HS uses exit_zero_count which is generally higher than
>> clk_zero_count. So just directly used LP to HS which amounts to
>> saying that switching from HS to LP takes lesser time than switching
>> from LP to HS. I can/should add code to compute max of the two.
>
> This could go to a separate task if you don't have time right now,
>

Most likely I can do this as well. Will push the updated patch by
sometime tomorrow.

Regards
Shobhit