linux-kernel - Re: [PATCH v3 2/2] memory: ti-emif-sram: introduce relocatable suspend/resume handlers

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Date:   Fri, 11 Aug 2017 10:42:34 -0500
From:   Dave Gerlach <d-gerlach@...com>
To:     Santosh Shilimkar <santosh.shilimkar@...cle.com>,
        Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>
CC:     Russell King <linux@...linux.org.uk>,
        Rob Herring <robh+dt@...nel.org>,
        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>, Keerthy J <j-keerthy@...com>,
        Johan Hovold <johan@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v3 2/2] memory: ti-emif-sram: introduce relocatable
 suspend/resume handlers

Russell/Johan,
On 08/01/2017 01:08 PM, Santosh Shilimkar wrote:
> On 7/26/2017 9:54 AM, Santosh Shilimkar wrote:
>>
>> On 7/24/2017 2:24 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 making use of the ARM
>>> asm-offsets file. In the same header that we define our data structures
>>> in we also define all the macros in an inline function and by adding a
>>> call to this in the asm_offsets file all macros are properly generated
>>> and available to the assembly code without cluttering up the asm-offsets
>>> file.
>>>
>>> Signed-off-by: Dave Gerlach <d-gerlach@...com>
>>> ---
> [...]
> 
>>>
>>>   arch/arm/kernel/asm-offsets.c    |   4 +
>>>   drivers/memory/Kconfig           |  10 ++
>>>   drivers/memory/Makefile          |   4 +
>>>   drivers/memory/emif.h            |  17 ++
>>>   drivers/memory/ti-emif-pm.c      | 339 
>>> +++++++++++++++++++++++++++++++++++++++
>>>   drivers/memory/ti-emif-sram-pm.S | 334 
>>> ++++++++++++++++++++++++++++++++++++++
>>>   include/linux/ti-emif-sram.h     | 147 +++++++++++++++++
>>>   7 files changed, 855 insertions(+)
>>>   create mode 100644 drivers/memory/ti-emif-pm.c
>>>   create mode 100644 drivers/memory/ti-emif-sram-pm.S
>>>   create mode 100644 include/linux/ti-emif-sram.h
>>>
>> I will need RMKs blessing since he reviewed the ASM code.
>>
>> Also need work out how to line this up. Typically I use to get
>> driver/memory patches via Greg's driver-core but this is more
>> PM code than memory driver and very SOC specific.
>>
>> Hi Arnd/Olof,
>> Will you be ok to pull this via arm-soc ? There is also follow
>> up platform PM code and DTS series which will make use of this.
>>
> Looks like I missed to copy Olof. Let me know guys if you are
> ok to pull this into your driver-soc given the dependencies.

Any additional comments here? I believe I have addressed everything from v2 so
hopefully this is acceptable now.

Regards,
Dave

> 
> Regards
> Santosh
>