linux-kernel - Re: [PATCH 1/4] drm/dsi: Add flag for continuous clock behavior

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Date:	Fri, 4 Jul 2014 14:57:21 +0900
From:	Alexandre Courbot <gnurou@...il.com>
To:	Andrzej Hajda <a.hajda@...sung.com>
Cc:	Alexandre Courbot <acourbot@...dia.com>,
	Thierry Reding <thierry.reding@...il.com>,
	Terje Bergstrom <tbergstrom@...dia.com>,
	Stephen Warren <swarren@...dotorg.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH 1/4] drm/dsi: Add flag for continuous clock behavior

Hi Andrejz,

On Thu, Jul 3, 2014 at 5:23 PM, Andrzej Hajda <a.hajda@...sung.com> wrote:
>
> Hi Alexandre,
>
> Thanks for the patch.
>
> On 07/02/2014 02:19 PM, Alexandre Courbot wrote:
>> As per section 5.6.1 of the DSI specification, all DSI transmitters must
>> support continuous clock behavior on the clock lane, while non-continuous
>> mode support is only optional. Add a flag that allows devices to indicate
>> that they require continuous clock mode to operate properly.
>>
>> Signed-off-by: Alexandre Courbot <acourbot@...dia.com>
>> ---
>>  include/drm/drm_mipi_dsi.h | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/include/drm/drm_mipi_dsi.h b/include/drm/drm_mipi_dsi.h
>> index 944f33f..5913ef4 100644
>> --- a/include/drm/drm_mipi_dsi.h
>> +++ b/include/drm/drm_mipi_dsi.h
>> @@ -94,6 +94,8 @@ void mipi_dsi_host_unregister(struct mipi_dsi_host *host);
>>  #define MIPI_DSI_MODE_VSYNC_FLUSH    BIT(8)
>>  /* disable EoT packets in HS mode */
>>  #define MIPI_DSI_MODE_EOT_PACKET     BIT(9)
>> +/* use continuous clock behavior on the clock lane */
>> +#define MIPI_DSI_MODE_CLOCK_CONTINUOUS       BIT(10)
>>
>
> According to MIPI DSI specification "All DSI transmitters and receivers
> shall support continuous clock behavior on the Clock Lane, and
> optionally may support non-continuous clock behavior". It suggests that
> continuous clock should be default behavior. So maybe better is to
> introduce sth like:
> +#define MIPI_DSI_MODE_CLOCK_NON_CONTINUOUS     BIT(10)

I started under the assumption that current host drivers assumed
non-continuous clock (as the Tegra driver currently does). In that
light, it seemed to make sense (and to be less intrusive) to introduce
that flag as a restriction rather than a capability. But if you think
this should be a capability I am not strongly against it - either way,
host drivers need to be changed to take that flag into account.
--
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