linux-kernel - Re: [PATCH 2/3] dt-bindings: add binding for at91-usart in spi mode

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Date:   Thu, 19 Apr 2018 13:04:16 +0300
From:   Radu Pirea <radu.pirea@...rochip.com>
To:     Mark Brown <broonie@...nel.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>
CC:     Nicolas Ferre <nicolas.ferre@...rochip.com>, <robh+dt@...nel.org>,
        <mark.rutland@....com>, <linux-kernel@...r.kernel.org>,
        <linux-spi@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH 2/3] dt-bindings: add binding for at91-usart in spi mode

On Tue, 2018-04-17 at 12:03 +0100, Mark Brown wrote:
> On Fri, Apr 13, 2018 at 08:12:51PM +0200, Alexandre Belloni wrote:
> > On 13/04/2018 19:12:54+0200, Nicolas Ferre wrote:
> > > This layout of the hardware is completely different from the
> > > USART one and
> > > it seems to makes sense to address it with a different hardware
> > > description
> > > and so a different compatible string.
> > But then, you can end up with two drivers trying to use the same IP
> > because nothing prevents you from writing a DT with both a usart
> > and an
> > spi node enabled for the same IP. request_mem_region() will not
> > help
> > here because then the working driver will depend on the probing
> > order.
> 
> We don't really have too much in the way of better ideas for how to
> handle this though.  Take a look at how the PXA SSP stuff handles
> this,
> though that's not really doing too much different it at least layers
> a
> mechanism on top to avoid collisions.
Hi Mark,

Thank you for suggestions. I followed your advice and looked at PXA SSP
driver. In my opinion it is a layer that avoids collsions and
unfortunately complicates things a bit. My ideea is to keep the things
as simple as possible. For example, I can enhance usart-serial and
usart-spi drivers to print detailed messages if probe fails because one
driver tries to request a memory region already used by another driver.
What do you think? Is this approach a good way to move forward?