Date: Tue, 10 Mar 2015 00:25:02 -0300 From: Luiz Otavio O Souza <lists.br@gmail.com> To: Milan Obuch <freebsd-arm@dino.sk> Cc: "freebsd-arm@freebsd.org" <freebsd-arm@freebsd.org> Subject: Re: Raspberry Pi and PiTFT display - problem with driver Message-ID: <CAB=2f8z_Gp-bQCs7%2BKDmngYC3rnrd4iEWMbZyypGZjJhbf7VJg@mail.gmail.com> In-Reply-To: <20150308204438.18f403a1@zeta.dino.sk> References: <20150308204438.18f403a1@zeta.dino.sk>
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On 8 March 2015 at 16:44, Milan Obuch wrote:
> Hi,
>
> I am trying to write a driver for PiTFT display, small 320x240 pixel
> panel with touch screen. From software perspective, there are two
> devices, touch screen controller with GPIO expander, STMPE610, and TFT
> display controller/driver, ILI9341. Both are connected via SPI bus,
> with one GPIO pin for the later.
>
> This is where a problem is - I found a way how to use SPI bus to
> program STMPE610, how to read and write to its register, at present,
> read chip identification and set/reset GPIO used to control LED
> backlight. I did it a bit hackish for now, using sysctl, but it is
> simple to use and works. Definitive aproach should be to create a child
> device, gpioc, possibly, but it is much more complicated and takes more
> time to do.
>
> ILI9341, on the other side, uses SPI with GPIO, so there is a question
> how to do this - and, because this GPIO pin is used as 'command byte
> flag', it is quite vital for proper function.
>
> So, first, how can I describe this requirement in FDT? Currently, I
> just put there simple fragment:
>
> spi0 {
> ili0 {
> compatible = "st,ili";
> spi-chipselect = <0>;
> };
>
> tsc0 {
> compatible = "st,stmpe_tc";
> spi-chipselect = <1>;
> };
> };
>
> but this does not descibe fact ILI9341 uses one GPIO pin, in case of
> PiTFT, GPIO 25. It is in some way similar to what gpioiic does, but
> there is only one parent device, while I have two, spi bus and gpio
> pin... I need some hint...
>
> Second, I need some way to 'acquire' this pin in driver, so it is not
> possible to change its status with gpioctl, and obtain correct values
> for use in GPIOBUS_PIN_* calls to set pin's value.
>
> Third, it is not yet clear to me how would be the best way to implement
> this. According the docs, ILI9341 is programmed with series of short
> data exchanges, with exactly one command byte send to device, being
> flagged with active DC pin (connected to GPIO 25), followed with short
> series of bytes being written to device or, in case of status read and
> similar, being read from device, all with DC pin being inactive. DC is
> short for 'data/command'.
>
> Anybody out there with some hint? I will try to write something working
> first, which will be surely not nice at the beginning, but it is much
> easier to change something you know a bit about already...
>
> Regards,
> Milan
Hi,
If you need help with the GPIO expander on STMPE610, let me know.
Whenever is possible, we should try to use the default/vendor DTS for device.
I think this is the one used by PiTFT:
https://github.com/notro/fbtft/blob/master/dts/rpi.dts
[...]
&spi0 {
pitft@0{
compatible = "ilitek,ili9340";
reg = <0>;
status = "disabled";
spi-max-frequency = <32000000>;
rotate = <90>;
bgr;
buswidth = <8>;
dc-gpios = <&gpio 25 0>;
[...]
In this case you can make use of ofw_gpiobus_parse_gpios() to parse
the 'dc-gpios' property, here is an usage example:
http://pastebin.com/4mbZFuv1
The struct gpiobus_pin contains everything you need to manipulate the
GPIO pin (as in the example).
Luiz
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