linux-kernel - Re: [PATCH v5 3/4] drivers: firmware: xilinx: Add sysfs interface

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Date:   Thu, 1 Mar 2018 14:44:11 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Jolly Shah <jolly.shah@...inx.com>
Cc:     ard.biesheuvel@...aro.org, mingo@...nel.org,
        gregkh@...uxfoundation.org, matt@...eblueprint.co.uk,
        hkallweit1@...il.com, keescook@...omium.org,
        dmitry.torokhov@...il.com, michal.simek@...inx.com,
        robh+dt@...nel.org, mark.rutland@....com,
        Sudeep Holla <sudeep.holla@....com>, rajanv@...inx.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, Jolly Shah <jollys@...inx.com>
Subject: Re: [PATCH v5 3/4] drivers: firmware: xilinx: Add sysfs interface



On 20/02/18 19:21, Jolly Shah wrote:
> Add Firmware-ggs sysfs interface which provides read/write
> interface to global storage registers.
> 
> Signed-off-by: Jolly Shah <jollys@...inx.com>
> Signed-off-by: Rajan Vaja <rajanv@...inx.com>
> ---
>  .../ABI/stable/sysfs-driver-zynqmp-firmware        |  50 ++++
>  drivers/firmware/xilinx/zynqmp/Makefile            |   2 +-
>  drivers/firmware/xilinx/zynqmp/firmware-ggs.c      | 297 +++++++++++++++++++++
>  drivers/firmware/xilinx/zynqmp/firmware.c          |  13 +
>  include/linux/firmware/xilinx/zynqmp/firmware.h    |   2 +
>  5 files changed, 363 insertions(+), 1 deletion(-)
>  create mode 100644 Documentation/ABI/stable/sysfs-driver-zynqmp-firmware
>  create mode 100644 drivers/firmware/xilinx/zynqmp/firmware-ggs.c
> 
> diff --git a/Documentation/ABI/stable/sysfs-driver-zynqmp-firmware b/Documentation/ABI/stable/sysfs-driver-zynqmp-firmware
> new file mode 100644
> index 0000000..b04727a
> --- /dev/null
> +++ b/Documentation/ABI/stable/sysfs-driver-zynqmp-firmware
> @@ -0,0 +1,50 @@
> +What:		/sys/devices/platform/zynqmp-firmware/ggs> +Date:		January 2018
> +KernelVersion:	4.15.0
> +Contact:	"Jolly Shah" <jollys@...inx.com>
> +Description:
> +		Read/Write PMU global general storage register value,
> +		GLOBAL_GEN_STORAGE{0:3}.
> +		Global general storage register that can be used
> +		by system to pass information between masters.
> +

What kind of information ? Is there any semantics for that ?
Why does EEMI lack APIs for that if it's critical, giving access to
such information to userspace may not be good idea.

> +		The register is reset during system or power-on
> +		resets. Three registers are used by the FSBL and
> +		other Xilinx software products: GLOBAL_GEN_STORAGE{4:6}.
> +

FSBL ?

For what is it used ?

> +		Usage:
> +		# cat /sys/.../zynqmp-firmware/ggs0
> +		# echo <mask> <value> > /sys/.../zynqmp-firmware/ggs0
> +
> +		Example:
> +		# cat /sys/.../zynqmp-firmware/ggs0
> +		# echo 0xFFFFFFFF 0x1234ABCD > /sys/.../zynqmp-firmware/ggs0
> +
> +Users:		Xilinx
> +
> +What:		/sys/devices/platform/zynqmp-firmware/pggs*
> +Date:		January 2018
> +KernelVersion:	4.15.0
> +Contact:	"Jolly Shah" <jollys@...inx.com>
> +Description:
> +		Read/Write PMU persistent global general storage register
> +		value, PERS_GLOB_GEN_STORAGE{0:3}.
> +		Persistent global general storage register that
> +		can be used by system to pass information between
> +		masters.
> +

Ditto

> +		This register is only reset by the power-on reset
> +		and maintains its value through a system reset.
> +		Four registers are used by the FSBL and other Xilinx
> +		software products: PERS_GLOB_GEN_STORAGE{4:7}.
> +		Register is reset only by a POR reset.
> +

Ditto

-- 
Regards,
Sudeep