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

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Date:   Tue, 4 Apr 2017 09:11:52 -0700
From:   Tony Lindgren <tony@...mide.com>
To:     Russell King <linux@...linux.org.uk>
Cc:     Rob Herring <robh+dt@...nel.org>,
        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>, Dave Gerlach <d-gerlach@...com>
Subject: Re: [PATCH 2/2] memory: ti-emif-sram: introduce relocatable
 suspend/resume handlers

Russell,

* Dave Gerlach <d-gerlach@...com> [170328 13:57]:
> 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    |   6 +
>  drivers/memory/Kconfig           |  10 ++
>  drivers/memory/Makefile          |   4 +
>  drivers/memory/emif.h            |  17 ++
>  drivers/memory/ti-emif-pm.c      | 295 ++++++++++++++++++++++++++++++++++
>  drivers/memory/ti-emif-sram-pm.S | 334 +++++++++++++++++++++++++++++++++++++++
>  include/linux/ti-emif-sram.h     | 143 +++++++++++++++++
>  7 files changed, 809 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
> 
> diff --git a/arch/arm/kernel/asm-offsets.c b/arch/arm/kernel/asm-offsets.c
> index 608008229c7d..d728b5660e36 100644
> --- a/arch/arm/kernel/asm-offsets.c
> +++ b/arch/arm/kernel/asm-offsets.c
> @@ -28,6 +28,7 @@
>  #include <asm/vdso_datapage.h>
>  #include <asm/hardware/cache-l2x0.h>
>  #include <linux/kbuild.h>
> +#include <linux/ti-emif-sram.h>
>  
>  /*
>   * Make sure that the compiler and target are compatible.
> @@ -183,5 +184,10 @@ int main(void)
>  #ifdef CONFIG_VDSO
>    DEFINE(VDSO_DATA_SIZE,	sizeof(union vdso_data_store));
>  #endif
> +#if defined(CONFIG_SOC_AM33XX) || defined(CONFIG_SOC_AM43XX)
> +  BLANK();
> +  ti_emif_offsets();
> +#endif
> +
>    return 0; 
>  }

Does the above look OK to you?

Regards,

Tony