linux-kernel - Re: [PATCH v5 2/2] memory: ti-emif-sram: introduce relocatable suspend/resume handlers

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Date:   Mon, 16 Oct 2017 08:31:59 -0700
From:   Santosh Shilimkar <santosh.shilimkar@...cle.com>
To:     Russell King <linux@...linux.org.uk>
Cc:     Dave Gerlach <d-gerlach@...com>, Tony Lindgren <tony@...mide.com>,
        Santosh Shilimkar <ssantosh@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-omap@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>, Keerthy J <j-keerthy@...com>,
        Johan Hovold <johan@...nel.org>
Subject: Re: [PATCH v5 2/2] memory: ti-emif-sram: introduce relocatable
 suspend/resume handlers

Hi Russell,

On 10/13/2017 1:59 PM, Dave Gerlach wrote:
> Certain SoCs like Texas Instruments AM335x and AM437x require parts
> of the EMIF PM code to run late in the suspend sequence from SRAM,
> such as saving and restoring the EMIF context and placing the memory
> into self-refresh.
> 
> One requirement for these SoCs to suspend and enter its lowest power
> mode, called DeepSleep0, is that the PER power domain must be shut off.
> Because the EMIF (DDR Controller) resides within this power domain, it
> will lose context during a suspend operation, so we must save it so we
> can restore once we resume. However, we cannot execute this code from
> external memory, as it is not available at this point, so the code must
> be executed late in the suspend path from SRAM.
> 
> This patch introduces a ti-emif-sram driver that includes several
> functions written in ARM ASM that are relocatable so the PM SRAM
> code can use them. It also allocates a region of writable SRAM to
> be used by the code running in the executable region of SRAM to save
> and restore the EMIF context. It can export a table containing the
> absolute addresses of the available PM functions so that other SRAM
> code can branch to them. This code is required for suspend/resume on
> AM335x and AM437x to work.
> 
> In addition to this, to be able to share data structures between C and
> the ti-emif-sram-pm assembly code, we can automatically generate all of
> the C struct member offsets and sizes as macros by processing
> emif-asm-offsets.c into assembly code and then extracting the relevant
> data as is done for the generated platform asm-offsets.h files.
> 
> Signed-off-by: Dave Gerlach <d-gerlach@...com>
> ---
> v4->v5:
> * Simplify Makefile to generate include/generated/ti-emif-asm-offsets.h
> 
If you are happy with this version from Dave, can I get your ack please?
I can add this to the driver-soc then.

Regards,
Santosh