RPI 7" display touch controller

Fri Dec 10 18:41:42 UTC 2021

On Fri, 10 Dec 2021 at 18:20, Tim Harvey <tharvey at gateworks.com> wrote:
>
> On Thu, Nov 18, 2021 at 12:52 PM Tim Harvey <tharvey at gateworks.com> wrote:
> >
> > On Thu, Nov 18, 2021 at 10:30 AM Dave Stevenson
> > <dave.stevenson at raspberrypi.com> wrote:
> > >
> > > On Thu, 18 Nov 2021 at 17:36, Tim Harvey <tharvey at gateworks.com> wrote:
> > > >
> > > > On Thu, Nov 18, 2021 at 6:28 AM Dave Stevenson
> > > > <dave.stevenson at raspberrypi.com> wrote:
> > > > >
> > > > > Hi Tim
> > > > >
> > > > > On Thu, 18 Nov 2021 at 01:26, Tim Harvey <tharvey at gateworks.com> wrote:
> > > > > >
> > > > > > Greetings,
> > > > > >
> > > > > > I'm trying to get a RPI 7" touchscreen display working on an IMX8MM
> > > > > > board and while I've been able to get the MIPI DSI display and
> > > > > > backlight working I still can't seem to figure out the touch
> > > > > > controller.
> > > > > >
> > > > > > It's supposed to have an FT5406 controller on it without an interrupt
> > > > > > so I added polling support drivers/input/touchscreen/edt-ft5x06.c
> > > > > > which I was able to verify using another touchscreen with that
> > > > > > controller but when reading data from the FT5406 on the RPI controller
> > > > > > the data does not make sense.
> > > > > >
> > > > > > These panels appear to route the I2C from the FT5406 to a STM32F103
> > > > > > MPU that then provides a different I2C slave interface to the 15pin
> > > > > > connector that I'm connected to. On that I2C interface I see an i2c
> > > > > > slave at 0x45 which is managed by the regulator driver Marek wrote
> > > > > > (drivers/regulator/rpi-panel-attiny-regulator.c) and there is also an
> > > > > > i2c slave at 0x38 which I assumed was the FT5406 but I believe the MPU
> > > > > > is perhaps obfuscating that touch data.
> > > > > >
> > > > > > Anyone have any ideas on how to make that touch controller useful?
> > > > >
> > > > > There should be nothing unusual. 0x38 is the EDT touch controller.
> > > > > Starting with the Raspberry Pi OS Bullseye release, we're now using
> > > > > the panel directly from DRM rather than through the firmware. That's
> > > > > based on the branch at
> > > > > https://github.com/raspberrypi/linux/tree/rpi-5.10.y/
> > > > >
> > > >
> > > > Dave,
> > > >
> > > > That sounds like the driver that made it into mainline with Eric's
> > > > commit 2f733d6194bd ("drm/panel: Add support for the Raspberry Pi 7"
> > > > Touchscreen."). I looked there but that driver just deals with the DSI
> > > > and not with touch.
> > >
> > > No, we've reverted away from that driver as it exposes no regulator
> > > framework either, so again the touch element loses power.
> > >
> > > > > I also added polling support to edt-ft5x04.c.
> > > > > For DT, it uses a combination of the overlays vc4-kms-v3d,
> > > > > vc4-kms-dsi-7inch, and that includes edt-ft5406.dtsi, all of which are
> > > > > in /arch/arm/boot/dts/overlays
> > > >
> > > > It doesn't look like you ever submitted your edt-ft5x04 polling mode
> > > > support upstream. I saw another series to add polling support
> > > > submitted by Nicolas back in 2019 but was never followed up on
> > > > (https://patchwork.kernel.org/project/linux-input/list/?series=112187&archive=both).
> > >
> > > No I haven't as it's been crazy trying to get this lot to work under
> > > KMS at all over the last couple of months.
> > >
> > > > I have updated Nicolas' patch with the changes requested and am happy
> > > > to submit it upstream. The benefit of his patch is that it uses a dt
> > > > binding for the polling interval. I'm happy to submit this upstream.
> > >
> > > I hadn't seen Nicolas' patches, hence implementing it myself.
> > >
> > > If you've implemented the requested changes, could you check that the
> > > polling rate is as expected? We were seeing that the input framework
> > > wasn't delivering the requested poll rate when CONFIG_HZ=100 is
> > > defined in the config. I must confess that I haven't checked it on my
> > > current patch, but it was on my list of things to do.
> > > There was a report that "bd88ce25335d Input: raspberrypi-ts - switch
> > > to using polled mode of input devices" dropped the polling rate from
> > > the desired 60Hz in switching to that framework.
> >
> > Ok, I'll make a note to test that and submit it.
> >
> > >
> > > > >
> > > > > The main issue I had was configuring the regulator framework
> > > > > appropriately to allow the touch controller power to be separate from
> > > > > the bridge power. Without that if DRM powered down the panel it killed
> > > > > the touch controller too, and the touch driver never reinitialised
> > > > > itself.
> > > >
> > > > I'm using the same drivers/regulator/rpi-panel-attiny-regulator.c
> > > > regulator driver from mainline that Marek added as the power-supply
> > > > for the panel as well as the backlight controller. It looks like the
> > > > version in the rpi-5.10.y has several patches on top of it so I'll
> > > > take a look at those differences to see if it may be affecting the
> > > > touchscreen controller. It's really strange to me that the touch
> > > > controller's I2C goes through the STM32F103 MPU (as in the MPU's I2C
> > > > master connects to the touchscreen controller and a different MPU I2C
> > > > bus presents the touch controller like they are translating
> > > > something?).
> > >
> > > The touchscreen I2C does NOT go through the STM.
> > > The TS interrupt line does feed into the STM, but it's not actually used.
> > > The TC358762 I2C does go through the STM, but it isn't used other than
> > > a kick to bring the bridge out of reset.
> >
> > Ok, I've determined the DFROBOT Rpi displays do differ from the
> > official Rpi 7in display.
> >
> > Official 7in RPI display:
> > - I can't find a schematic anywhere for the official display but I an
> > ohmmeter confirms your claim that the touch controller I2C is
> > connected to the 15pin display I2C.
> > - I do not see the ft5406 at 0x38 on the i2c bus until I send a command a
> > REG_POWERON cmdto the ATTINY at 0x45 'i2c dev 2 && i2c mw 0x45 0x85 1 1'
> > in u-boot
> > - I must disable the rpi-panel-attiny-regulator.c driver as its probe
> > disables REG_POWERON and the linux driver won't see the FT5406
> > - The linux edt-ft5x06.c driver with polling added works fine and
> > gives me expected touch events
> >
> > With the DFROBOT 5in and 7in displays:
> > - the touch interface I2C does not connect directly to the 15pin
> > connector's I2C (shown in the schematic at schematic:
> > https://github.com/DFRobot/Wiki/raw/master/DFR0550_Schematics.pdf and
> > also verified with an ohmeter)
> > - I see the ft5406 at 0x38 on the i2c bus regardless of setting or
> > clearing REG_POWERON on the ATTINY at 0x45
> > - The linux edt-ft5x06.c driver with polling added gives me data that
> > does not make sense for touch events
> >
> > So I can only assume the DFROBOT displays are doing something strange
> > but I'm not clear how what they are doing is compatible with the RPI.
> > I guess I have to get an RPI, hook it up and see if the touch screen
> > works with the rpi 5.10.y kernel.
> >
> > >
> > > > I wonder if I'm hitting that reinitialization issue. Do you recall any
> > > > details about that? Was it that the driver returned seemingly invalid
> > > > touch data like I'm getting or did it just not respond?
> > >
> > > If the power goes down then all the registers written during probe [1]
> > > are reset. I don't recall exactly what the data then contained, but I
> > > did get a load of I2C transactions fail with -EREMOTEIO as the
> > > messages weren't ACKed.
> > >
> > > [1] https://elixir.bootlin.com/linux/latest/source/drivers/input/touchscreen/edt-ft5x06.c#L1207
> > >
> > > > Silly question likely but how do I power down the DRM portion to test
> > > > to see if it affects the touch controller?
> > >
> > > xrandr --output DSI-1 --off
> > > There must be a libdrm call to do the equivalent, but I'll admit that
> > > I can't think of an existing tool that implements it.
> >
> > do you know of a sysfs way to do this or something that doesn't require xrandr?
> >
> > >
> > > > > On our branch rpi-panel-attiny-regulator.c has been updated to control
> > > > > those functions independently as GPIOs, which then get used via
> > > > > regulator-fixed, or as reset-gpios.
> > > > > Telling both bridge and touch that they shared a regulator didn't work
> > > > > as the DSI bridge seems mildly fussy about the DSI state when it is
> > > > > powered up.
> > > >
> > > > Hmm... I wonder if this is the problem I had with the 'official' rpi
> > > > 7in display that I never got working. I did get the DFROBOT rpi 5in
> > > > and 7in displays working.
> > >
> > > I'm not that familiar with the DFRobot displays.
> > > I have tried an Osoyoo 3.5" panel [2] that pretends to be the Pi
> > > panel, and it looks similar. Reality is that it uses a Lattice FPGA to
> > > convert from DSI to DPI. All the LP configuration commands sent to it
> > > are ignored. Startup requirements of that compared to the Toshiba are
> > > unknown.
> > >
> > > [2] https://www.amazon.co.uk/OSOYOO-Capacitive-Connector-Resolution-Raspberry/dp/B087WVC1J2
> > >
> > > > > Hope that helps.
> > > > >
> > > >
> > > > The fact you tell me that the rpi-5.10.y branch goes away from the
> > > > strange 'firmware' driver I found at
> > > > https://github.com/raspberrypi/linux/blob/rpi-4.2.y/drivers/input/touchscreen/rpi-ft5406.c
> > > > and uses the standard ft5406.c driver (with polling mode added) is
> > > > very helpful in that I feel I have a hope of getting this working.
> > >
> > > I have one of our panels working in front of me using my patched
> > > version of edt-ft5x06 as the driver for the touch element.
> > >
> > > > Does the rpi-5.10.y kernel work for the official rpi 7in display as
> > > > well as the DFROBOT displays as far as you know?
> > >
> > > As above, I'm not aware of DFRobot.
> > > With the Osoyoo I can't recall exactly what it was doing with I2C. I
> > > think it only really responded to the ID command and PWM for the
> > > backlight. The reset and power control that is required on our boards
> > > isn't really relevant to them.
> > > I was doing i2cset -y -f <bus> 0x45 0x85 [1|0] to turn power on/off,
> > > and I seem to recall it did nothing.
> >
> > Right... this is also the same with the DFROBOT touchscreen displays.
> >
> > I do really like the build quality, availability, and pricing of the
> > DFROBOT displays but also a huge advantage is that they derive power
> > from the 15pin connector 3.3V pins so there are no other connections.
> > Their backlight doesn't appear to be controllable via PWM however and
> > instead they have a manual brightness thumbwheel on them.
> >
> > The other advantage for me at the moment is that I still haven't
> > gotten the official RPI 7in display to work with the IMX8MM (no pixels
> > displayed) where as the DFROBOT one is working for me.
> >
> > > ...
> > > Just for you I fired it up. It ACKs all I2C addresses just for a
> > > laugh, and indeed it takes no action on 0x85, only 0x86 (for PWM), and
> > > reading 0x80 (ID).
> > >
> >
>
> Dave,
>
> After some more investigation I've found that while the DFRobot
> DRF0550 and DFR0678 touch controller does not work with the ft5x06
> driver it does indeed work on a Rpi with the raspberrypi-ts driver. So
> from an Rpi perspective the latest OS image doesn't work but the
> 'Legacy' OS image does (which appears to have the same 5.10 kernel but
> uses legacy drivers?).

You have to love cloned devices.
Have you checked with DFRobot as to what the actual touchscreen
controller chip is?

> So if I understand correctly the Rpi has some firmware that talks over
> I2C and translates touch events from this 'legacy API' over to a
> memory mapped area. How can I learn about this firmware and what kind
> of translation it does to make these touch controllers work on a non
> rpi?

It does very little different from edt-ft5x06.

At an I2C level it reads register 0x02 of the touchscreen controller
to get the current number of points, and then does that number of 4
byte reads for register (3+6*i) to get the touch information.
The edt-ft5x06 driver just reads all registers from 0 to generally
0x21 to get all points in one hit. It then parses all the point
information instead of looking at the reported number of points.

There are a couple more commits to our kernel tree for edt-ft5x06 as
we were seeing some issues.
The main one is that it seems unreliable in reporting TOUCH_UP events.
Whilst it's implemented explicitly in the driver with the current
patches, I believe it could be done via the INPUT_MT_DROP_UNUSED flag
if input_mt_sync_frame is used as well. When time allows I was
intending to upstream that fix.

  Dave