linux-kernel - Re: [PATCH v2 4/7] ARM: davinci: Add support for an L3RAM gen

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Date:	Mon, 1 Oct 2012 09:56:03 -0400
From:	Matt Porter <mporter@...com>
To:	Sekhar Nori <nsekhar@...com>
Cc:	Linux DaVinci Kernel List 
	<davinci-linux-open-source@...ux.davincidsp.com>,
	Paul Walmsley <paul@...an.com>,
	Russell King <linux@....linux.org.uk>,
	Benoit Cousson <b-cousson@...com>,
	Tony Lindgren <tony@...mide.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Hans J. Koch" <hjk@...sjkoch.de>,
	Linux OMAP List <linux-omap@...r.kernel.org>,
	Linux ARM Kernel List <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 4/7] ARM: davinci: Add support for an L3RAM gen_pool

On Mon, Oct 01, 2012 at 08:32:42AM -0400, Matt Porter wrote:
> On Mon, Oct 01, 2012 at 05:34:02PM +0530, Sekhar Nori wrote:
> > Hi Matt,
> > 
> > On 9/29/2012 1:07 AM, Matt Porter wrote:
> > > L3RAM (shared SRAM) is needed for use by several drivers.
> > > This creates a genalloc pool and a hook for the platform code
> > > to provide the struct gen_pool * in platform data.
> > > 
> > > Signed-off-by: Matt Porter <mporter@...com>
> > 
> > I am not sure if any of the DaVinci devices have a need to allocate from
> > *both* ARM RAM and shared RAM. Shared RAM is not present on all DaVinci
> > devices AFAIR, and on DA850, there is just 8KB ARM RAM so I am not sure
> > if there is much point in trying to allocate from there.
> > 
> > Can you instead see if Ben's earlier patch[1] to use shared RAM for SRAM
> > allocation on DA850 makes sense for your case? If yes, can you repost
> > with Ben's patch included in your series instead of this patch? I would
> > prefer that over creating a new pool for shared RAM.
> 
> Hrm, I did look at Ben's earlier patch. The reason I added a separate
> pool mostly was so I didn't have to touch the PM code at all. That can
> continue using the private SRAM API with the ARM RAM as it is now. The
> idea here was to allow that to be separate since no other bus masters
> can access the ARM RAM anyway and do something that didn't require
> regression testing PM. Also, I figured there's really no reason to use
> even a tiny bit of the shared SRAM on PM if we have that ARM RAM there
> and working fine for that use case.
> 
> The other thing is that Ben's patch needs to be rewritten to at least
> have the hook I added so we can provide the gen_pool in platform data.
> If you prefer this path still, I can add the needed hook on top of his
> original patch. Ultimately, I only *need* genalloc support for the
> shared sram so I can remove the private SRAM API from uio_pruss...so I'm
> happy with any way to get at it.
> 
> Oh, and to be honest...it's not just for uio_pruss, but also to cleanly
> remove the private SRAM API usage from the davinci ASoC driver too.

[and replying to myself :)]

Looking at the older parts (DM355/365/DM64xx) in more detail now, I see
that to get rid of SRAM API in davinci ASoC, we'll have a similar hook
to get the local ARM RAM gen_pool pointer necessary to support ping-pong
to that pool since that's able to be accessed from EDMA on those parts.
Ultimately, the approach is the same, it's just a matter of if we want
to fully leverage both SRAM pools on DA850 and friends.

-Matt
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