linux-kernel - Re: [PATCH v2 6/8] drm: Introduce drm_bridge_mode

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Date:   Fri, 12 May 2017 16:20:07 +0530
From:   Archit Taneja <architt@...eaurora.org>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        dri-devel@...ts.freedesktop.org
Cc:     Jose Abreu <Jose.Abreu@...opsys.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
        linux-kernel@...r.kernel.org,
        Carlos Palminha <CARLOS.PALMINHA@...opsys.com>
Subject: Re: [PATCH v2 6/8] drm: Introduce drm_bridge_mode_valid()



On 05/12/2017 03:08 PM, Laurent Pinchart wrote:
> Hi Daniel,
>
> On Wednesday 10 May 2017 17:14:33 Daniel Vetter wrote:
>> On Wed, May 10, 2017 at 04:41:09PM +0300, Ville Syrjälä wrote:
>>> On Tue, May 09, 2017 at 06:00:13PM +0100, Jose Abreu wrote:
>>>> Introduce a new helper function which calls mode_valid() callback
>>>> for all bridges in an encoder chain.
>>>>
>>>> Signed-off-by: Jose Abreu <joabreu@...opsys.com>
>>>> Cc: Carlos Palminha <palminha@...opsys.com>
>>>> Cc: Alexey Brodkin <abrodkin@...opsys.com>
>>>> Cc: Ville Syrjälä <ville.syrjala@...ux.intel.com>
>>>> Cc: Daniel Vetter <daniel.vetter@...ll.ch>
>>>> Cc: Dave Airlie <airlied@...ux.ie>
>>>> Cc: Andrzej Hajda <a.hajda@...sung.com>
>>>> Cc: Archit Taneja <architt@...eaurora.org>
>>>> ---
>>>>
>>>>  drivers/gpu/drm/drm_bridge.c | 33 +++++++++++++++++++++++++++++++++
>>>>  include/drm/drm_bridge.h     |  2 ++
>>>>  2 files changed, 35 insertions(+)
>>>>
>>>> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
>>>> index 86a7637..dc8cdfe 100644
>>>> --- a/drivers/gpu/drm/drm_bridge.c
>>>> +++ b/drivers/gpu/drm/drm_bridge.c
>>>> @@ -206,6 +206,39 @@ bool drm_bridge_mode_fixup(struct drm_bridge
>>>> *bridge,
>>>>
>>>>  EXPORT_SYMBOL(drm_bridge_mode_fixup);
>>>>
>>>>  /**
>>>>
>>>> + * drm_bridge_mode_valid - validate the mode against all bridges in the
>>>> + * 			   encoder chain.
>>>> + * @bridge: bridge control structure
>>>> + * @mode: desired mode to be validated
>>>> + *
>>>> + * Calls &drm_bridge_funcs.mode_valid for all the bridges in the
>>>> encoder
>>>> + * chain, starting from the first bridge to the last. If at least one
>>>> bridge + * does not accept the mode the function returns the error
>>>> code.
>>>> + *
>>>> + * Note: the bridge passed should be the one closest to the encoder.
>>>> + *
>>>> + * RETURNS:
>>>> + * MODE_OK on success, drm_mode_status Enum error code on failure
>>>> + */
>>>> +enum drm_mode_status drm_bridge_mode_valid(struct drm_bridge *bridge,
>>>> +					   const struct drm_display_mode
> *mode)
>>>> +{
>>>> +	enum drm_mode_status ret = MODE_OK;
>>>> +
>>>> +	if (!bridge)
>>>> +		return ret;
>>>> +
>>>> +	if (bridge->funcs->mode_valid)
>>>> +		ret = bridge->funcs->mode_valid(bridge, mode);
>>>> +
>>>> +	if (ret != MODE_OK)
>>>> +		return ret;
>>>> +
>>>> +	return drm_bridge_mode_valid(bridge->next, mode);
>>>
>>> Looks like it should be pretty trivial to avoid the recursion.
>>>
>>> Am I correct in interpreting this that bridges have some kind of
>>> a hand rolled linked list implementation? Reusing the standard
>>> linked lists would allow you to use list_for_each() etc.
>>
>> Yeah it's a hand-rolled list, but current hw also has a bridge nesting
>> depth of 2, so it really doesn't matter. I guess once we have real long
>> chains of bridges we can fix this (and just using list_head sounds like a
>> great idea).
>
> Even if not really needed right now, it's a pretty easy cleanup, if Jose has
> time to handle it in v3 of this series let's not postpone it ;-)

jfyi, some of the bridge functions call the ops from the last bridge in the
chain to first, so we'd need to use list_for_each_entry_prev() (or something
like that) for them.

Archit

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