lkml.org 
[lkml]   [2019]   [Aug]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: [PATCH 2/2] DTS: ARM: gta04: introduce legacy spi-cs-high to make display work again
    On Fri, Jul 26, 2019 at 12:43 AM Rob Herring <robh@kernel.org> wrote:
    > On Thu, Jul 25, 2019 at 12:23 AM H. Nikolaus Schaller <hns@goldelico.com> wrote:

    > > 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.

    I agree. The background on it is here:
    https://lkml.org/lkml/2019/4/2/4

    Not using the negatively defined (i.e. if it is no there, the line is
    by default active low) spi-cs-high would break
    PowerPC, who were AFAICT using this to ship devices.

    Yours,
    Linus Walleij

    \
     
     \ /
      Last update: 2019-08-05 12:31    [W:2.477 / U:0.252 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site