On Thu, Jul 25, 2019 at 12:23 AM H. Nikolaus Schaller <hns@xxxxxxxxxxxxx> wrote: > > Hi Rob, > > > Am 24.07.2019 um 21:42 schrieb Rob Herring <robh@xxxxxxxxxx>: > > > > On Mon, Jul 08, 2019 at 04:46:05PM +0200, H. Nikolaus Schaller wrote: > >> commit 6953c57ab172 "gpio: of: Handle SPI chipselect legacy bindings" > >> > >> did introduce logic to centrally handle the legacy spi-cs-high property > >> in combination with cs-gpios. This assumes that the polarity > >> of the CS has to be inverted if spi-cs-high is missing, even > >> and especially if non-legacy GPIO_ACTIVE_HIGH is specified. > >> > >> The DTS for the GTA04 was orginally introduced under the assumption > >> that there is no need for spi-cs-high if the gpio is defined with > >> proper polarity GPIO_ACTIVE_HIGH. > > > > Given that spi-cs-high is called legacy, that would imply that DT's > > should not have to use spi-cs-high. > > Yes. > > > > >> This was not a problem until gpiolib changed the interpretation of > >> GPIO_ACTIVE_HIGH and missing spi-cs-high. > > > > Then we should fix gpiolib... > > I tried to convince Linus that this is the right way but he convinced > me that a fix that handles all cases does not exist. > > There seem to be embedded devices with older DTB (potentially in ROM) > which provide a plain 0 value for a gpios definition. And either with > or without spi-cs-high. > > Since "0" is the same as "GPIO_ACTIVE_HIGH", the absence of > spi-cs-high was and must be interpreted as active low for these > devices. This leads to the inversion logic in code. > > AFAIR it boils down to the question if gpiolib and the bindings > should still support such legacy devices with out-of tree DTB, > but force in-tree DTS to add the legacy spi-cs-high property. > > Or if we should fix the 2 or 3 cases of in-tree legacy cases > and potentially break out-of tree DTBs. If it is small number of platforms, then the kernel could handle those cases explicitly as needed. > IMHO it is more general to keep the out-of-tree DTBs working > and "fix" what we can control (in-tree DTS). If we do this, then we need to not call spi-cs-high legacy because we're stuck with it forever. Rob
