[Intel-gfx] [PATCH resend 07/15] drm/i915/dsi: Drop bogus MIPI_SEQ_ASSERT_RESET before POWER_ON

[Hans de Goede]

Hi,

On 24-02-17 18:00, Bob Paauwe wrote:
> On Mon, 20 Feb 2017 15:08:37 +0100
> Hans de Goede <hdegoede at redhat.com> wrote:
>
>> MIPI_SEQ_ASSERT_RESET before POWER_ON is not necessary for 2 reasons:
>> 1) The reset should already be asserted before intel_dsi_pre_enable()
>>    gets called
>> 2) Most (some?) VBTs will ensure reset was asserted in their
>>    MIPI_SEQ_DEASSERT_RESET themselves
>>
>> Signed-off-by: Hans de Goede <hdegoede at redhat.com>
>
> Using words like "should" and some? don't inspire a lot of confidence
> that this is the right thing to do. Is there some way to verify that
> these two conditions are true?

Well the i915 code should never call intel_dsi_[pre_]enable without
first having called intel_dsi_post_disable() which does:

intel_dsi_exec_vbt_sequence(intel_dsi, MIPI_SEQ_ASSERT_RESET);

Already, also this is undoing a recent (4.9 kernel IIRC) change,
before that the i915 did not call the MIPI_SEQ_ASSERT_RESET
sequence from the enable path. Also doing this is against the VBT
spec.

Regards,

Hans



>
>> ---
>>  drivers/gpu/drm/i915/intel_dsi.c | 1 -
>>  1 file changed, 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_dsi.c b/drivers/gpu/drm/i915/intel_dsi.c
>> index 78d5884..4ebf308 100644
>> --- a/drivers/gpu/drm/i915/intel_dsi.c
>> +++ b/drivers/gpu/drm/i915/intel_dsi.c
>> @@ -669,7 +669,6 @@ static void intel_dsi_pre_enable(struct intel_encoder *encoder,
>>  	/* put device in ready state */
>>  	intel_dsi_device_ready(encoder);
>>
>> -	intel_dsi_exec_vbt_sequence(intel_dsi, MIPI_SEQ_ASSERT_RESET);
>>  	intel_dsi_exec_vbt_sequence(intel_dsi, MIPI_SEQ_POWER_ON);
>>  	intel_dsi_exec_vbt_sequence(intel_dsi, MIPI_SEQ_DEASSERT_RESET);
>>  	intel_dsi_exec_vbt_sequence(intel_dsi, MIPI_SEQ_INIT_OTP);
>
>
>