Hi Nikolaus, On Tue, Dec 1, 2020 at 12:13 PM H. Nikolaus Schaller <h...@goldelico.com> wrote: > > Am 01.12.2020 um 17:53 schrieb Sven Van Asbroeck <thesve...@gmail.com>: > > On Tue, Dec 1, 2020 at 11:43 AM H. Nikolaus Schaller <h...@goldelico.com> > > wrote: > >> > >> You are right. It is active low. > >> > > > > In that case, we have a very simple solution, just remove the spi-cs-high, > > and things will work. > > We originally had it that way and because there was a change in gpiolib we had > to introduce it.
The current rules re. spi chip-selects in devicetrees are here: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpio/gpiolib-of.c?h=v5.10-rc6#n191 This is the way I see things: - according to the current rules, your devicetree describes a spi panel with an active-high chip select - the actual chip select of your panel is active-low - a spi/gpiod bug inverted the chip-select in many instances - because of this bug, your devicetree happened to work before 766c6b63aa04 - 766c6b63aa04 ("spi: fix client driver breakages when using GPIO descriptors") fixes this chip-select polarity bug - you now need to remove your devicetree work-around for this bug by reverting f1f028ff89cb0d3 > > I am not sure if DT maintainers accept that we revert a DT change just to > handle some change in a driver. Usually they insist on fixing a driver and > live with the DT. DT is carved in stone or could be ROM... This is above my paygrade, but I've always assumed that the devicetree ABI is an in-kernel ABI, i.e. not a userspace ABI. Meaning that it is flexible and there is no obligation to keep it 100% backwards compatible. Of course Rob Herring may want to keep it as backwards-compatible as possible, but that's an altogether different thing from having a userspace-type ABI. > > So you could try to submit a revert of f1f028ff89cb0d3 with a description > why it is needed. And please make sure that it is also applied where your > patch is backported to stable. So it should have some > > Fixes: 766c6b63aa04 ("spi: fix client driver breakages when using GPIO > descriptors") I have no insight in your devicetrees, and no hardware to test it out either. As a user of these trees, you are best placed to make the change and test it out. I invite you to submit a patch (revert of f1f028ff89cb0d3) to the mailing list. > > > So you mean you are just restoring the behaviour before > > 6953c57ab172 > > was introduced? > That was based on my incorrect interpretation of the devicetree spi cs rules, my apologies. I have linked to the correct rules in the link above.
