Date:	Tue, 25 Feb 2014 10:22:45 -0600
From:	Rob Herring <robherring2@...il.com>
To:	Joel Fernandes <joelf@...com>
Cc:	Mark Rutland <mark.rutland@....com>,
	Linux OMAP List <linux-omap@...r.kernel.org>,
	"nsekhar@...com" <nsekhar@...com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux ARM Kernel List <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] ARM: EDMA: Use platform_get_resource functions for DT

On Fri, Feb 21, 2014 at 11:36 AM, Joel Fernandes <joelf@...com> wrote:
> On 02/21/2014 06:15 AM, Mark Rutland wrote:
>>> Also, while at it get rid of the assumption in the code that "CC" is at reg
>>> index 0 in the DT and xbar is at offset 1. Instead use reg-names to get the
>>> memory resource in concern keeping things much cleaner and simpler. This also
>>> makes it possible to have multiple channel controllers.
>>
>> While this is nice I think we have to have a fallback to the existing
>> behaviour if there's no reg-names property present, unless we know for
>> certain no-one is possibly using an existing DTB.
>
> Yes, its true it break existing DTBs but currently only 2 TI SoCs use EDMA this
> way, the vast majority of EDMA users are yet to follow where we can do it right.
>  Further, the old bindings are really limiting specially the 2 CC case and if
> additionally memory maps are used in the future. So keeping the old binding is
> limiting in this regard.
>
> Here is what the platform_data used to look like when used by mach-davinci:
>
> static struct resource da850_edma_resources[] = {
>         {
>                 .name   = "edma_cc0",
>                 .start  = DA8XX_TPCC_BASE,
>                 .end    = DA8XX_TPCC_BASE + SZ_32K - 1,
>                 .flags  = IORESOURCE_MEM,
>         },
>         {
>                 .name   = "edma_tc0",
>                 .start  = DA8XX_TPTC0_BASE,
>                 .end    = DA8XX_TPTC0_BASE + SZ_1K - 1,
>                 .flags  = IORESOURCE_MEM,
>         },
>         {
>                 .name   = "edma_tc1",
>                 .start  = DA8XX_TPTC1_BASE,
>                 .end    = DA8XX_TPTC1_BASE + SZ_1K - 1,
>                 .flags  = IORESOURCE_MEM,
>         },
>         {
>                 .name   = "edma_cc1",
>                 .start  = DA850_TPCC1_BASE,
>                 .end    = DA850_TPCC1_BASE + SZ_32K - 1,
>                 .flags  = IORESOURCE_MEM,
>         },
>
> As you can see, there are several memory maps and different interpretations.
> Considering this, IMO- it makes sense to pay a small price to keep the semantics
> sane.

Then do 1 compatible string per interpretation. That can then define
the number of CCs and TCs.

>
> On the other hand, the other 2 options are:
> 1. We add a fallback if reg-names look up fails.

reg-names is supposed to be optional, so you should already have that fallback.

Rob

> 2. We inject reg-names property into edma DT nodes that don't have them, and
> make sure all future dtsi with edma nodes mention the reg-names property.
>
> These 2 are a bit error prone though, for example if someone deliberately
> forgets to mention reg-names, and the code still works, but misbehaves in some way.
>
> Regards,
> -Joel
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Powered by blists - more mailing lists