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

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Message-ID: <CAPcSpELdAK6=O8HG9FJXG_t88eymZO1f3wxzFqmR-faUn4jx4g@mail.gmail.com>
Date:	Mon, 1 Oct 2012 09:50:11 -0400
From:	Ben Gardiner <bengardiner@...ometrics.ca>
To:	"Nori, Sekhar" <nsekhar@...com>, Matt Porter <mporter@...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>,
	Subhasish Ghosh <subhasish@...tralsolutions.com>
Subject: Re: [PATCH v2 4/7] ARM: davinci: Add support for an L3RAM gen_pool

On Mon, Oct 1, 2012 at 8:32 AM, Matt Porter <mporter@...com> 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.
> [...]

I agree with Matt. Preserving the use of the ARM RAM (8K on L138 -- as
you said, Sekhar) in any fashion is preferable to moving suspend
support into shared RAM. There is more of it (128K on L138) but also
more pressure on allocations there since there are more clients.

I appreciate that you are trying to preserve prior efforts in
attempted merging of SRAM support -- thank you for that; however, that
patch [1] was just an import of Subashish Ghosh's patch [2]  -- I
chose _that_ implementation option then mainly because I imagined it
would be the least risky to get accepted upstream and not because of
any particular technical merits.

Best Regards,
Ben Gardiner

[1] https://patchwork.kernel.org/patch/840552/
[2] https://patchwork.kernel.org/patch/549351/

---
Nanometrics Inc.
http://www.nanometrics.ca
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