[PATCH 2/3] drm/panel: Add DT bindings for Ilitek ILI9322

Wed Sep 20 11:56:38 UTC 2017

On Sat, Sep 2, 2017 at 11:17 PM, Linus Walleij <linus.walleij at linaro.org> wrote:
> On Thu, Aug 17, 2017 at 10:44 PM, Rob Herring <robh at kernel.org> wrote:
>> On Sun, Aug 13, 2017 at 01:44:47PM +0200, Linus Walleij wrote:
>
>>> This adds device tree bindings for the Ilitek ILI9322
>>> 320x240 TFT panel driver.
>>>
>>> Cc: devicetree at vger.kernel.org
>>> Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
> (...)
>>> +Optional properties:
>>> +  - width-mm: physical panel width [mm]
>>> +  - height-mm: physical panel height [mm]
>>> +  - vcc-supply: core voltage supply, see regulator/regulator.txt
>>> +  - iovcc-supply: voltage supply for the interface input/output signals,
>>> +    see regulator/regulator.txt
>>> +  - vci-supply: voltage supply for analog parts, see regulator/regulator.txt
>>> +  - reset-gpios: a GPIO spec for the reset pin, see gpio/gpio.txt
>>> +  - ilitek,vreg1out-microvolt: the output in microvolts for the VREGOUT1
>>> +    regulator used to drive the physical display. Valid ranges are 3600 thru
>>> +    6000 in 100 microvolt increments. If not specified, hardware defaults will
>>> +    be used (4.5V).
>>> +  - ilitek,vcom-amplitude-percent: the percentage of VREGOUT1 used for the
>>> +    peak-to-peak amplitude of the communcation signals to the physical display.
>>> +    Valid ranges are 70 thru 132 percent in increments if two percent. Odd
>>> +    percentages will be truncated. If not specified, hardware defaults will be
>>> +    used (114%).
>>> +  - ilitek,vcom-high-percent: the percentage of VREGOUT1 used for the peak
>>> +    voltage on the communications link. Valid ranges are 37 thru 100 percent.
>>> +    If not specified, hardware defaults will be used (91%).
>>> +  - ilitek,gamma-correction-neg: a set of 8 nybbles describing negative
>>> +    gamma correction for voltages V1 thru V8. Valid range 0..15
>>> +  - ilitek,gamma-correction-pos: a set of 8 nybbles describing positive
>>> +    gamma correction for voltages V1 thru V8. Valid range 0..15
>>> +    These adjust what grayscale voltage will be output for input data V1 = 0,
>>> +    V2 = 16, V3 = 48, V4 = 96, V5 = 160, V6 = 208, V7 = 240 and V8 = 255.
>>> +    The curve is shaped like this:
>>> +
>>> +    ^
>>> +    |                                                        V8
>>> +    |                                                   V7
>>> +    |                                          V6
>>> +    |                               V5
>>> +    |                    V4
>>> +    |            V3
>>> +    |     V2
>>> +    | V1
>>> +    +----------------------------------------------------------->
>>> +      0   16     48      96         160        208      240  255
>>> +
>>> +    The negative and postive gamma values adjust the V1 thru V8 up/down
>>> +    according to the datasheet specifications. This is a property of the
>>> +    physical display connected to the display controller and may vary.
>>> +    If defined, both arrays must be supplied in full. If the properties
>>> +    are not supplied, hardware defaults will be used.
>>
>> Normally, we the physical panel is described which would imply all these
>> settings. Are there lots of panels with this controller that would
>> justify all these settings?
>
> The datasheet for the ili9322 just says it "drives panels" essentially.
> Googling around gives at hand that it is used pretty frequently in
> Shenzhen China for adapting different off-the-shelf panels to
> different inputs.
>
> I can't really answer how many of these products that run one or
> another OS using device tree to describe the configuration. It feels more
> like I'm paving the road for others to travel.
>
> Probably other Ilitek panel adapters will need something similar.
>
>>> +  - ilitek,entry-mode: the panel can be connected to various input streams
>>> +    and four of them can be selected by electronic straps on the display.
>>> +    However it is possible to select another mode or override the
>>> +    electronic default with this property. Valid values:
>>> +    0: 8 bit serial RGB through
>>> +    1: 8 bit serial RGB aligned
>>> +    2: 8 bit serial RGB dummy 320x240
>>> +    3: 8 bit serial RGB dummy 360x240
>>> +    4: disabled
>>> +    5: 24 bit parallel RGB through
>>> +    6: 24 bit parallel RGB aligned
>>> +    7: 24 bit YUV 640Y 320CbCr
>>> +    8: 24 bit YUV 720Y 360CbCr
>>> +    9: disabled
>>> +    10: 8 bit ITU-R BT.656 720Y 360CbCr
>>> +    11: 8 bit ITU-R BT.656 640Y 320CbCr
>>
>> To some extent, we have some standard bindings to describe this.
>
> I don't find any. Maybe I'm looking in the wrong places :(
>
> These are closest associated with the DRM "media bus formats"
> in Linux include/uapi/linux/media-bus-format.h
> such as:
>
> #define MEDIA_BUS_FMT_RGB444_1X12               0x1016
> #define MEDIA_BUS_FMT_RGB444_2X8_PADHI_BE       0x1001
> #define MEDIA_BUS_FMT_RGB444_2X8_PADHI_LE       0x1002
> #define MEDIA_BUS_FMT_RGB555_2X8_PADHI_BE       0x1003
> #define MEDIA_BUS_FMT_RGB555_2X8_PADHI_LE       0x1004
> #define MEDIA_BUS_FMT_RGB565_1X16               0x1017
> #define MEDIA_BUS_FMT_BGR565_2X8_BE             0x1005
> #define MEDIA_BUS_FMT_BGR565_2X8_LE             0x1006
> #define MEDIA_BUS_FMT_RGB565_2X8_BE             0x1007
> #define MEDIA_BUS_FMT_RGB565_2X8_LE             0x1008
> #define MEDIA_BUS_FMT_RGB666_1X18               0x1009
> #define MEDIA_BUS_FMT_RBG888_1X24               0x100e
> #define MEDIA_BUS_FMT_RGB666_1X24_CPADHI        0x1015
> #define MEDIA_BUS_FMT_RGB666_1X7X3_SPWG         0x1010
> (...)
>
> We can surely regard this bus format list as standard and
> copy and extend it in DT (it does not have ITU-R formats for
> the moment) but I don't know if that is wise.
>
> Also the input modes of ili9322 is coupled with resolution so
> it would need two more cells or so for resolution so I feel
> it would over-complicate things for these 12 enumerators.

Can we proceed with these patches?

Any opinion from DT or panel maintainers?

Yours,
Linus Walleij