linux-kernel - Re: [PATCH] ARM: at91: at91sam9x5: sets NPCS0 (PA14) back to GPIO

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Date:	Fri, 25 Jul 2014 13:34:26 +0200
From:	Boris BREZILLON <boris.brezillon@...e-electrons.com>
To:	jiri.prchal@...ignal.cz
Cc:	Bo Shen <voice.shen@...el.com>, nicolas.ferre@...el.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org
Subject: Re: [PATCH] ARM: at91: at91sam9x5: sets NPCS0 (PA14) back to GPIO

On Fri, 25 Jul 2014 12:32:38 +0200
Jiří Prchal <jiri.prchal@...ignal.cz> wrote:

> 
> 
> Dne 25.7.2014 v 12:18 Boris BREZILLON napsal(a):
> >> / # devmem 0xfffff408
> >> 0xF0E04018
> >> / # devmem 0xfffff418
> >> 0xE0C04000
> >> / # devmem 0xfffff438
> >> 0x00C04000
> >> / # devmem 0xfffff43c
> >> 0x13FFD7FB
> >> / # devmem 0xfffff458
> >> 0x00000000
> >> / # devmem 0xfffff468
> >> 0xFF223B4E
> >> / # devmem 0xfffff470
> >> 0x0F000000
> >> / # devmem 0xfffff474
> >> 0x00000000
> >> / # devmem 0xfffff498
> >> 0xFFFFFFFF
> >>
> >> I get thought if is possible that in time of probe fm25 (it's first) is not configured PA14 (it 's last)?
> >
> > Oh, nice catch!
> > I think you've found the origin of this bug.
> > Indeed each device is instantiated sequentially and thus when the first
> > device is probed (CS0) the last one has not requested it's cs_gpio yet
> > (and PA14 is still assigned to periph A).
> >
> > Declaring cs-pins and referencing them in pinctrl-0 solves the issue
> > because in this case all CS pins are requested during controller probe.
> >
> So, what would be the right fix up? I my patch it's not good idea since some other driver can request pin for other 
> peripheral earlier than spi. In board dts it could be new investigating for someone else who don't know this issue. I 
> think the best way would be request all cs in early spi init since cs depends on each other and must be all of them in 
> right state before any communication on bus. They are part of bus, like miso, mosi, clk, not part of chips. Also they 
> are defined in parent spi node, not in child chip node.
> Am I right?

Yes, you can take a look at [1] as an example.

[1]http://lxr.free-electrons.com/source/drivers/spi/spi-efm32.c#L361


-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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