linux-kernel - Re: [PATCH v2 3/3] drm/panel-simple: allow LVDS format override

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Message-ID: <039bda0d-c478-ce80-9328-a024ed847ba1@pengutronix.de>
Date:   Mon, 5 Jun 2023 08:20:26 +0200
From:   Johannes Zink <j.zink@...gutronix.de>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Sam Ravnborg <sam@...nborg.org>,
        kernel test robot <lkp@...el.com>,
        Dan Carpenter <error27@...il.com>,
        patchwork-jzi@...gutronix.de, kernel@...gutronix.de,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] drm/panel-simple: allow LVDS format override

Hi Laurent,

thanks for your review and your feedback.

On 6/2/23 17:39, Laurent Pinchart wrote:
> Hi Johannes,
> 
> Thank you for the patch.
> 
> On Tue, May 23, 2023 at 10:19:43AM +0200, Johannes Zink wrote:
>> Some panels support multiple LVDS data mapping formats, which can be
>> used e.g. run displays on jeida-18 format when only 3 LVDS lanes are
>> available.
>>
>> Add parsing of an optional data-mapping devicetree property, which also
>> touches up the bits per color to match the bus format.
> 
> Of course one could argue that the innolux,g101ice-l01 panel should have
> used the panel-lvds bindings... :-)

I would prefer to add it in the panel-simple, if ever possible, as this already 
has the timing information etc. in the driver. I would probably opt to use the 
panel-lvds for an entirely new LVDS display, but as the innolux,g101ice-l01 is 
already supported in panel-simple, imho there should be no harm in supporting 
the jeida-18 operating mode as well. Also other displays in panel-simple 
_might_ benefit from supporting non-default LVDS mapping modes, though I have 
not researched whether they have actual hardware support for doing so.

> 
>> Signed-off-by: Johannes Zink <j.zink@...gutronix.de>
>>
>> ---
>>
>> Changes:
>>
>>    v1 -> v2: - fix missing unwind goto found by test robot
>>                Reported-by: kernel test robot <lkp@...el.com>
>>                Reported-by: Dan Carpenter <error27@...il.com>
>>                Link: https://lore.kernel.org/r/202304160359.4LHmFOlU-lkp@intel.com/
>> ---
>>   drivers/gpu/drm/panel/panel-simple.c | 39 +++++++++++++++++++++++++++++++++++-
>>   1 file changed, 38 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
>> index 2a9c1a785a5c..0a35fdb49ccb 100644
>> --- a/drivers/gpu/drm/panel/panel-simple.c
>> +++ b/drivers/gpu/drm/panel/panel-simple.c
>> @@ -40,6 +40,7 @@
>>   #include <drm/drm_edid.h>
>>   #include <drm/drm_mipi_dsi.h>
>>   #include <drm/drm_panel.h>
>> +#include <drm/drm_of.h>
>>   
>>   /**
>>    * struct panel_desc - Describes a simple panel.
>> @@ -559,7 +560,7 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc)
>>   	struct device_node *ddc;
>>   	int connector_type;
>>   	u32 bus_flags;
>> -	int err;
>> +	int err, ret;
>>   
>>   	panel = devm_kzalloc(dev, sizeof(*panel), GFP_KERNEL);
>>   	if (!panel)
>> @@ -605,6 +606,42 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc)
>>   			panel_simple_parse_panel_timing_node(dev, panel, &dt);
>>   	}
>>   
>> +
> 
> Double blank line.

ack, gonna fix in v3.

> 
>> +	/* optional data-mapping property for overriding bus format */
> 
> s/optional/Optional/

ack, gonna fix in v3.

> 
>> +	ret = drm_of_lvds_get_data_mapping(dev->of_node);
>> +	if (ret == -EINVAL) {
>> +		dev_warn(dev, "Ignore invalid data-mapping property");
>> +	} else if (ret != -ENODEV) {
> 
> If someone incorrectly sets the property in DT for a non-LVDS panel,
> the result won't be nice. That's of course a DT issue, but I wonder if
> we could/should protect against it. You could move this code to a
> separate function (which would have the added benefit of lowering the
> indentation level as you can return early in error cases), and call it
> from panel_simple_probe() only if the panel is an LVDS panel (as
> reported by its desc->bus_format value).
> 

that's a good idea, gonna change it for v3.

>> +		int bpc;
>> +
>> +		switch (ret) {
>> +		default:
>> +			WARN_ON(1);
>> +			fallthrough;
>> +		case MEDIA_BUS_FMT_RGB888_1X7X4_SPWG:
>> +			fallthrough;
>> +		case MEDIA_BUS_FMT_RGB888_1X7X4_JEIDA:
>> +			bpc = 8;
>> +			break;
>> +		case MEDIA_BUS_FMT_RGB666_1X7X3_SPWG:
>> +			bpc = 6;
>> +		}
>> +
>> +		if (desc->bpc != bpc || desc->bus_format != ret) {
>> +			struct panel_desc *override_desc;
>> +
>> +			override_desc = devm_kmemdup(dev, desc, sizeof(*desc), GFP_KERNEL);
>> +			if (!override_desc) {
>> +				err = -ENOMEM;
>> +				goto free_ddc;
>> +			}
>> +
>> +			override_desc->bus_format = ret;
>> +			override_desc->bpc = bpc;
>> +			panel->desc = override_desc;
>> +		}
>> +	}
>> +
>>   	connector_type = desc->connector_type;
>>   	/* Catch common mistakes for panels. */
>>   	switch (connector_type) {
> 

-- 
Pengutronix e.K.                | Johannes Zink                  |
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