linux-kernel - Re: [PATCH] arm64: dts: rockchip: add spiX aliases for rk3399

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Date:	Tue, 19 Jul 2016 12:27:54 -0700
From:	Brian Norris <briannorris@...omium.org>
To:	Heiko Stübner <heiko@...ech.de>
Cc:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-rockchip@...ts.infradead.org,
	Brian Norris <computersforpeace@...il.com>,
	linux-arm-kernel@...ts.infradead.org,
	Caesar Wang <wxt@...k-chips.com>
Subject: Re: [PATCH] arm64: dts: rockchip: add spiX aliases for rk3399

+ Rob

Hi,

On Tue, Jul 19, 2016 at 08:56:47PM +0200, Heiko Stuebner wrote:
> Am Dienstag, 19. Juli 2016, 08:39:55 schrieb Uwe Kleine-König:
> > On Thu, Jul 14, 2016 at 06:24:33PM -0700, Brian Norris wrote:
> > > It's nicer to see this:
> > >     # ls -l /sys/bus/spi/devices/
> > >     total 0
> > >     lrwxrwxrwx 1 root root 0 Dec 31  1969 spi0.0 ->
> > >     ../../../devices/platform/ff1c0000.spi/spi_master/spi0/spi0.0
> > >     lrwxrwxrwx 1 root root 0 Dec 31  1969 spi1.0 ->
> > >     ../../../devices/platform/ff1d0000.spi/spi_master/spi1/spi1.0
> > >     lrwxrwxrwx 1 root root 0 Dec 31  1969 spi2.0 ->
> > >     ../../../devices/platform/ff1e0000.spi/spi_master/spi2/spi2.0
> > >     lrwxrwxrwx 1 root root 0 Dec 31  1969 spi5.0 ->
> > >     ../../../devices/platform/ff200000.spi/spi_master/spi5/spi5.0> 
> > > than this:
> > >     # ls -l /sys/bus/spi/devices/
> > >     total 0
> > >     lrwxrwxrwx 1 root root 0 Dec 31  1969 spi32763.0 ->
> > >     ../../../devices/platform/ff200000.spi/spi_master/spi32763/spi32763.0
> > >     lrwxrwxrwx 1 root root 0 Dec 31  1969 spi32764.0 ->
> > >     ../../../devices/platform/ff1e0000.spi/spi_master/spi32764/spi32764.0
> > >     lrwxrwxrwx 1 root root 0 Dec 31  1969 spi32765.0 ->
> > >     ../../../devices/platform/ff1d0000.spi/spi_master/spi32765/spi32765.0
> > >     lrwxrwxrwx 1 root root 0 Dec 31  1969 spi32766.0 ->
> > >     ../../../devices/platform/ff1c0000.spi/spi_master/spi32766/spi32766.0> 
> > > With the latter, it's much clearer which bus devices are on.
> > > 
> > > Signed-off-by: Brian Norris <briannorris@...omium.org>
> > > ---
> > > 
> > >  arch/arm64/boot/dts/rockchip/rk3399.dtsi | 6 ++++++
> > >  1 file changed, 6 insertions(+)
> > > 
> > > diff --git a/arch/arm64/boot/dts/rockchip/rk3399.dtsi
> > > b/arch/arm64/boot/dts/rockchip/rk3399.dtsi index
> > > 4c84229789ef..b04abbfd4898 100644
> > > --- a/arch/arm64/boot/dts/rockchip/rk3399.dtsi
> > > +++ b/arch/arm64/boot/dts/rockchip/rk3399.dtsi
> > > @@ -70,6 +70,12 @@
> > > 
> > >  		serial2 = &uart2;
> > >  		serial3 = &uart3;
> > >  		serial4 = &uart4;
> > > 
> > > +		spi0 = &spi0;
> > > +		spi1 = &spi1;
> > > +		spi2 = &spi2;
> > > +		spi3 = &spi3;
> > > +		spi4 = &spi4;
> > > +		spi5 = &spi5;
> > 
> > Note that Rob Herring (with his dt-maintainer hat on) doesn't like these
> > aliases.
> > See for example:
> > 	http://mid.gmane.org/20160705140546.GA10601@rob-hp-laptop

But why? I believe half the arguments in the linked thread were
Catch-22's -- there were no "mainline" users (which is a false target
IMO anyway, as Christer Weinigel mentioned somewhere in the thread Rob
linked), and so we couldn't accept more documentation (or users) for the
feature. FWIW, my quick grep now shows there are currently 43 mainline
users.

This feature is very useful. Some of the thread Rob pointed to argued
that the indexing isn't HW documentation; in this case, it most
certainly is. The RK3399 TRM explicitly has these SPI buses named SPI0,
SPI1, SPI2, SPI3, SPI4, and SPI5, and schematics that I've seen use the
same terminology. It is therefore *much* nicer to have my device show up
as 'spi2.0' (reflecting their correct HW name) rather than spi32764.0.
Sometimes I can't even get as far as mounting sysfs to check what this
maps to, but having spi2.0 in the kernel log can clearly tell me what
device is causing problems.

If Rob can support a better alternative solution, I'd be happy to
switch. But I don't understand why we can't use a useful (not just to
me, but presumably to at least 43 other independent users, and many
more out of tree), existing, and long-supported feature here.

> thanks for the heads up on this. I've dropped this patch again.

:(

Regards,
Brian