linux-kernel - Re: [PATCH v3 2/2] firmware: arm_scmi: Support 'reg-io-width' property for shared memory

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Message-ID: <ZscW_E33YXF8Nx7r@bogus>
Date: Thu, 22 Aug 2024 11:46:21 +0100
From: Sudeep Holla <sudeep.holla@....com>
To: Florian Fainelli <florian.fainelli@...adcom.com>
Cc: linux-arm-kernel@...ts.infradead.org, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Sudeep Holla <sudeep.holla@....com>,
	Cristian Marussi <cristian.marussi@....com>,
	devicetree@...r.kernel.org (open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS),
	linux-kernel@...r.kernel.org (open list),
	arm-scmi@...r.kernel.org (open list:SYSTEM CONTROL & POWER/MANAGEMENT INTERFACE),
	justin.chen@...adcom.com, opendmb@...il.com,
	kapil.hali@...adcom.com, bcm-kernel-feedback-list@...adcom.com
Subject: Re: [PATCH v3 2/2] firmware: arm_scmi: Support 'reg-io-width'
 property for shared memory

Hi Florian,

Sorry for getting late to this party, I wasn't able to review this before.
Overall changes look correct. But my main concern is that is SCMI the right
place to have such IO accessors. It is better to run it through Arnd if
he is happy with it before I send him the pull request containing these.

On Fri, Aug 16, 2024 at 03:42:21PM -0700, Florian Fainelli wrote:
> Some shared memory areas might only support a certain access width,
> such as 32-bit, which memcpy_{from,to}_io() does not adhere to at least
> on ARM64 by making both 8-bit and 64-bit accesses to such memory.
>

Is this limitation on the hardware for both read and writes ?
The reason I ask is I see arm64 does have memcpy_toio_aligned() or
__iowrite32_copy_full() for 32 bit aligned writes.

-- 
Regards,
Sudeep