Messages in this thread | | | Subject | Re: Revert "video: fbdev: mxsfb: Remove driver" | From | Marek Vasut <> | Date | Tue, 17 Aug 2021 12:03:46 +0200 |
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On 8/17/21 11:08 AM, Alistair Francis wrote: > On Mon, Aug 16, 2021 at 5:55 PM Marek Vasut <marex@denx.de> wrote: >> >> On 8/16/21 9:34 AM, Alistair Francis wrote: >>> On Sun, Aug 15, 2021 at 10:31 PM Marek Vasut <marex@denx.de> wrote: >>>> >>>> On 8/15/21 2:16 PM, Alistair Francis wrote: >>>>> Hello, >>>>> >>>>> Commit f225f1393f034 "video: fbdev: mxsfb: Remove driver" removed the >>>>> mxsfb fbdev driver. >>>>> >>>>> I am now working on getting mainline Linux running on the reMarkable 2 >>>>> eInk reader [1]. Unfortunately the rM2 doesn't use the standard EPD >>>>> controller on the i.MX SoC, but instead uses the LCD controller. >>>>> >>>>> eInk panels are complex to control and require writing temperature >>>>> dependent waveforms. As these waveforms are proprietary [2] the rM >>>>> team runs closed source software called SWTCON in userspace to control >>>>> the panel [3]. >>>>> >>>>> This closed source software expects the fbdev mxsfb driver and it >>>>> doesn't work with the DRM mxsfb driver (at least not that I can get it >>>>> to). >>>>> >>>>> The NXP fork of Linux also re-adds the fbdev driver [4], so they also >>>>> see some uses for it. >>>>> >>>>> I was wondering if the community would be open to re-adding the fbdev >>>>> mxsfb driver to mainline? It could be re-added with a different >>>>> dt-binding so that it is not used by default and only enabled for >>>>> boards when required (like for the rM2). >>>>> >>>>> 1: https://remarkable.com/store/remarkable-2 >>>>> 2: https://goodereader.com/blog/e-paper/e-ink-waveforms-are-a-closely-guarded-secret >>>>> 3: https://remarkablewiki.com/tech/rm2_framebuffer >>>>> 4: https://source.codeaurora.org/external/imx/linux-imx/log/drivers/video/fbdev/mxsfb.c?h=lf-5.10.35-2.0.0 >>>> >>>> +CC Sam. >>>> >>>> What sort of special thing does your proprietary userspace do that >>>> cannot be added to the DRM driver or the fbdev emulation (if needed) ? >>> >>> It's hard to tell. When using the DRM driver I get cryptic errors >>> about the frame buffer not being available. >> >> Do you have fbdev emulation enabled ? Does /dev/fbX exist ? > > I do and /dev/fb0 exists > >> >> What sort of messages do you get and from where ? > > This is the error I get: > > xochitl[252]: Error writing variable information: Invalid argument...
Some ioctl returns -EINVAL maybe ? strace would tell you.
> xochitl is the proprietary userspace code. I don't really have a good > idea of what that error would mean. > > I also see this: > > Framebuffer has wrong id: "mxcfb"
Are you sure you're not confusing mxcfb (The freescale imx scanout engine) with mxsfb (The originally sgtl block, bought by freescale) ?
>> You could run strace on the application to see how it communicates with >> the old driver via the ioctl interface and compare it with the fbdev >> emulation on the new driver, maybe there is some odd ioctl which is not >> emulated. > > I had a quick look at this. > > xochitl does a lot more than just controls the display, it interacts > with lots of other hardware and strace produces a lot of logs. I also > don't see the error when manually starting it, only at boot (but it > still doesn't work). > > A quick run with > > strace -f xochitcl > > and I don't even see an access to /dev/fb0, so I'm not sure where the > accesses are coming from.
You can try writing the output of strace to file (strace -o) for easier analysis. Then grep for either access to /dev/fb0 (or any symlink to it which might exist), or search for the mxcfb string, maybe the application aborts even before opening the fbdev due to some other problem.
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