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

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Date:   Mon, 13 Nov 2017 09:07:33 -0800
From:   Santosh Shilimkar <santosh.shilimkar@...cle.com>
To:     Russell King - ARM Linux <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

On 11/10/2017 8:39 AM, Russell King - ARM Linux wrote:
> On Mon, Oct 16, 2017 at 08:31:59AM -0700, Santosh Shilimkar wrote:
>> 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.
> 
> Does it need my ack anymore?  It doesn't touch anything in arch/arm.
> If you still want it, then... notwithstanding the loss of type checking
> that fncpy() gave and the new sram stuff messes up...
> 
> Acked-by: Russell King <rmk+kernel@...linux.org.uk>
> 
Thanks Russell !!