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

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Message-Id: <ED6A6797-D1F9-473B-ABFF-B6951A924BC1@goldelico.com>
Date:   Mon, 16 Sep 2019 12:59:19 +0200
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Discussions about the Letux Kernel <letux-kernel@...nphoenux.org>,
        Rob Herring <robh@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        devicetree <devicetree@...r.kernel.org>,
        Linux-OMAP <linux-omap@...r.kernel.org>,
        Tony Lindgren <tony@...mide.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>,
        Benoît Cousson <bcousson@...libre.com>
Subject: Re: [Letux-kernel] [PATCH 2/2] DTS: ARM: gta04: introduce legacy spi-cs-high to make display work again

ping.

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@...nade.info>:
> 
> Hi,
> 
> On Mon, 5 Aug 2019 12:29:19 +0200
> Linus Walleij <linus.walleij@...aro.org> wrote:
> 
>> On Fri, Jul 26, 2019 at 12:43 AM Rob Herring <robh@...nel.org> wrote:
>>> On Thu, Jul 25, 2019 at 12:23 AM H. Nikolaus Schaller <hns@...delico.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