Re: [PATCH v6 10/14] drm/panel: add S6E3FA0 driver

[Thierry Reding <thierry.reding@gmail.com>]

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On Mon, Jul 21, 2014 at 10:56:08AM +0200, Andrzej Hajda wrote:
> On 07/18/2014 03:49 AM, YoungJun Cho wrote:
> > Hi Thierry,
> >
> > Thank you a lot for kind comments.
> >
> > On 07/17/2014 07:36 PM, Thierry Reding wrote:
> >> On Thu, Jul 17, 2014 at 06:01:25PM +0900, YoungJun Cho wrote:
> >> [...]
> >>> diff --git a/drivers/gpu/drm/panel/panel-s6e3fa0.c b/drivers/gpu/drm/panel/panel-s6e3fa0.c
> >> [...]
> >>> +/* Manufacturer Command Set */
> >>> +#define MCS_GLOBAL_PARAMETER	0xb0
> >>> +#define MCS_AID			0xb2
> >>> +#define MCS_ELVSSOPT		0xb6
> >>> +#define MCS_TEMPERATURE_SET	0xb8
> >>> +#define MCS_PENTILE_CTRL	0xc0
> >>> +#define MCS_GAMMA_MODE		0xca
> >>> +#define MCS_VDDM		0xd7
> >>> +#define MCS_ALS			0xe3
> >>> +#define MCS_ERR_FG		0xed
> >>> +#define MCS_KEY_LEV1		0xf0
> >>> +#define MCS_GAMMA_UPDATE	0xf7
> >>> +#define MCS_KEY_LEV2		0xfc
> >>> +#define MCS_RE			0xfe
> >>> +#define MCS_TOUT2_HSYNC		0xff
> >>> +
> >>> +/* Content Adaptive Brightness Control */
> >>> +#define DCS_WRITE_CABC		0x55
> >> Is this not a manufacturer specific command? I couldn't find it in the
> >> DSI or DCS specifications, but it sounds like something standard (also
> >> indicated by the DCS_ prefix). Can you point out the specification for
> >> this?
> >>
> > Andrzej commented before and decided it as DCS one because if the value 
> > is less than 0xb0, it is DCS one and the others are MCS one.
> > But still I'm not sure it is correct.
> I would not say 'decided'. I have just stated that according to DCS
> specification
> it should be DCS command (below 0xb0), but it is not present in mipi dcs
> specs.
> On the other side many panels have it [1]:
> 
> [1]:
> https://www.google.com/search?q=%22Write+Content+Adaptive+Brightness+Control%22

Yeah, my search yielded similar results. I wonder if this is perhaps
part of a draft future specification. I'll try to ask around some more
if anybody knows what the status of this is.

> >>> +static void s6e3fa0_read_mtp_id(struct s6e3fa0 *ctx)
> >>> +{
> >>> +	unsigned char id[MTP_ID_LEN];
> >>> +	int ret;
> >>> +
> >>> +	s6e3fa0_set_maximum_return_packet_size(ctx, MTP_ID_LEN);
> >>> +	ret = s6e3fa0_dcs_read(ctx, MIPI_DCS_GET_DISPLAY_ID, id, MTP_ID_LEN);
> >> This also looks like a standard DCS command. I can't find it in either
> >> v1.01 nor v1.02 of the specification, though. Do you know where it's
> >> specified?
> >>
> > Yes, I also can't find it in DCS specification and there is no special 
> > description in panel datasheet.
> > But as it is declared in "include/video/mipi_display.h", so I think it 
> > is a standard one.
> 
> On page 9 of the "Introduction of MIPI by Renesas" [2] there is info
> it is a part of "Nokia I/F command list", I guess it is kind of alpha
> version of MIPI DCS.
> 
> [2]: http://wenku.baidu.com/view/658fab68af1ffc4ffe47acbe.html

That link is the only one which contains "Nokia I/F command list" on the
internet (that is, according to Google). But since this is already part
of the mipi_display.h header file we may as well use it.

I wonder if perhaps the READ_DDB_START and READ_DDB_CONTINUE commands
could be used as a replacement for this display ID.

Adding Guennadi, Tomi, Paul and Imre on Cc since they were involved with
the original patch that added mipi_display.h. Perhaps they remember what
the origin of this command is.

Thierry

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