linux-kernel - Re: [PATCH v2 05/15] DMA: shdma: pass SoC-specific configuration to the driver via OF matching

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Date:	Tue, 23 Jul 2013 01:23:40 +0200
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
Cc:	linux-kernel@...r.kernel.org, linux-sh@...r.kernel.org,
	Magnus Damm <magnus.damm@...il.com>,
	Simon Horman <horms@...ge.net.au>,
	Vinod Koul <vinod.koul@...el.com>,
	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
Subject: Re: [PATCH v2 05/15] DMA: shdma: pass SoC-specific configuration to the driver via OF matching

Hi Guennadi,

On Monday 22 July 2013 09:29:40 Guennadi Liakhovetski wrote:
> On Mon, 22 Jul 2013, Laurent Pinchart wrote:
> > On Friday 19 July 2013 18:29:30 Guennadi Liakhovetski wrote:
> > > Similar to the non-DT case, this patch passes SoC-specific configuration
> > > to the driver via device ID matching, instead of platform data.
> > > 
> > > Signed-off-by: Guennadi Liakhovetski <g.liakhovetski+renesas@...il.com>
> > > ---
> > > 
> > > v2: adjust spacing within array definitions to keep a uniform style.
> > > 
> > >  Documentation/devicetree/bindings/dma/shdma.txt |    7 +++++--
> > >  drivers/dma/sh/shdmac.c                         |   22
> > >  +++++++++++++-------
> > >  2 files changed, 20 insertions(+), 9 deletions(-)
> > > 
> > > diff --git a/Documentation/devicetree/bindings/dma/shdma.txt
> > > b/Documentation/devicetree/bindings/dma/shdma.txt index c15994a..7702e35
> > > 100644
> > > --- a/Documentation/devicetree/bindings/dma/shdma.txt
> > > +++ b/Documentation/devicetree/bindings/dma/shdma.txt
> > > 
> > > @@ -22,7 +22,10 @@ Optional properties (currently unused):
> > >  * DMA controller
> > > 
> > >  Required properties:
> > > -- compatible:	should be "renesas,shdma"
> > > +- compatible:	should be one of
> > > +		"renesas,shdma-r8a73a4" for the system DMAC on r8a73a4 SoC
> > > +		"renesas,shdma-r8a7740" for the DMACs (not RTDMAC) on r8a7740
> > > +		"renesas,shdma" for a generic DMAC
> > > 
> > >  Example:
> > >  	dmac: dma-mux0 {
> > > 
> > > @@ -36,7 +39,7 @@ Example:
> > >  		ranges;
> > >  		
> > >  		dma0: shdma@...08020 {
> > > 
> > > -			compatible = "renesas,shdma";
> > > +			compatible = "renesas,shdma-r8a7740";
> > > 
> > >  			reg = <0xfe008020 0x270>,
> > >  			
> > >  				<0xfe009000 0xc>;
> > >  			
> > >  			interrupt-parent = <&gic>;
> > > 
> > > diff --git a/drivers/dma/sh/shdmac.c b/drivers/dma/sh/shdmac.c
> > > index 859ddbe..f80543c 100644
> > > --- a/drivers/dma/sh/shdmac.c
> > > +++ b/drivers/dma/sh/shdmac.c
> > > @@ -20,6 +20,8 @@
> > > 
> > >  #include <linux/init.h>
> > >  #include <linux/module.h>
> > > 
> > > +#include <linux/of.h>
> > > +#include <linux/of_device.h>
> > > 
> > >  #include <linux/slab.h>
> > >  #include <linux/interrupt.h>
> > >  #include <linux/dmaengine.h>
> > > 
> > > @@ -663,6 +665,14 @@ static const struct shdma_ops sh_dmae_shdma_ops = {
> > > 
> > >  	.get_partial = sh_dmae_get_partial,
> > >  
> > >  };
> > > 
> > > +static const struct of_device_id sh_dmae_of_match[] = {
> > > +	{.compatible = "renesas,shdma",},
> > > +	{.compatible = "renesas,shdma-r8a73a4", .data = 
r8a73a4_shdma_devid,},
> > > +	{.compatible = "renesas,shdma-r8a7740", .data = 
r8a7740_shdma_devid,},
> > 
> > Nit-picking here, OF device ID entries are usually ordered from most
> > specific to most generic compatible strings. It's up to you.
> 
> Yeah, in fact, I'm not even sure we need the generic line, so far I think
> we always need SoC configuration. Maybe I shall just remove it. Could do
> in an incremental patch.

If you end up sending a v3 you could remove the generic entry. Otherwise let's 
not bother for now.

> > > +	{}
> > > +};
> > > +MODULE_DEVICE_TABLE(of, sh_dmae_of_match);
> > 
> > Shouldn't you guard the table with #ifdef CONFIG_OF ? If the driver can
> > only be used on ARM platforms it might not be worth it, but if it can be
> > used on SH as well that would make sense.
> 
> Well, it is a pretty common practice, I admit, but what exactly does it
> bring us apart from saving a couple of bytes? I just tried a SuperH build
> - no problem.

Exactly that, saving a couple of bytes :-)

-- 
Regards,

Laurent Pinchart

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