[Letux-kernel] [PATCH 2/2] DTS: ARM: gta04: introduce legacy spi-cs-high to make display work again

H. Nikolaus Schaller hns at goldelico.com
Mon Sep 16 12:59:19 CEST 2019


Device omap3-gta04 is neither working with v5.3 nor linux-next quite a while and we need a solution.

> Am 31.08.2019 um 08:48 schrieb Andreas Kemnade <andreas at kemnade.info>:
> Hi,
> On Mon, 5 Aug 2019 12:29:19 +0200
> Linus Walleij <linus.walleij at linaro.org> wrote:
>> On Fri, Jul 26, 2019 at 12:43 AM Rob Herring <robh at kernel.org> wrote:
>>> On Thu, Jul 25, 2019 at 12:23 AM H. Nikolaus Schaller <hns at 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.
> is this thing now just waiting for someone to do a s/legacy//?
> Regards,
> Andreas

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