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

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Message-ID: <20121002161424.GP5641@beef>
Date:	Tue, 2 Oct 2012 12:14:24 -0400
From:	Matt Porter <mporter@...com>
To:	Sekhar Nori <nsekhar@...com>
Cc:	Linux DaVinci Kernel List 
	<davinci-linux-open-source@...ux.davincidsp.com>,
	Russell King <linux@....linux.org.uk>,
	Benoit Cousson <b-cousson@...com>,
	Tony Lindgren <tony@...mide.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Paul Walmsley <paul@...an.com>,
	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 Tue, Oct 02, 2012 at 03:32:55PM +0530, Sekhar Nori wrote:
> On 10/1/2012 6:02 PM, 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
> 
> But you dont have to touch the PM code. PM code can continue using SRAM
> API. I have verified in the past that PM can work using shared RAM.
> 
> > 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.
> 
> I see no reason why PM would break with shared RAM. I have not even seen
> reports of shared RAM being short of size so we need to save space by
> having PM code in ARM RAM. I can test the changes before the code is
> committed and it will get tested in linux-next as well.

Ok, sounds good to me.

> > 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.
> 
> Right, I prefer just adding the hook so that genalloc can be used along
> with SRAM API.
 
Ok.

> > 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.
> 
> Audio can use the shared RAM too. And once all users of the SRAM API are
> gone, only the hook to help pass the gen_pool as platform data needs to
> remain.

Right, I think we are on the same page now. I'll post an update to Ben's
original patch with required gen_pool hook for pdata use.

I noticed the beginning of DT support for davinci and the DT-based
genalloc driver, https://patchwork.kernel.org/patch/1421961/, fits
into that well.

-Matt
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