linux-kernel - Re: [PATCH 1/4] nvmem: sunxi_sid: Always use 32-bit MMIO reads

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Message-ID: <5410996.rnE6jSC6OK@diego>
Date:   Thu, 25 Aug 2022 14:05:08 +0200
From:   Heiko Stübner <heiko@...ech.de>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     Samuel Holland <samuel@...lland.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-sunxi@...ts.linux.dev, Samuel Holland <samuel@...lland.org>
Subject: Re: [PATCH 1/4] nvmem: sunxi_sid: Always use 32-bit MMIO reads

Am Sonntag, 14. August 2022, 19:36:52 CEST schrieb Samuel Holland:
> The SID SRAM on at least some SoCs (A64 and D1) returns different values
> when read with bus cycles narrower than 32 bits. This is not immediately
> obvious, because memcpy_fromio() uses word-size accesses as long as
> enough data is being copied.
> 
> The vendor driver always uses 32-bit MMIO reads, so do the same here.
> This is faster than the register-based method, which is currently used
> as a workaround on A64. And it fixes the values returned on D1, where
> the SRAM method was being used.
> 
> The special case for the last word is needed to maintain .word_size == 1
> for sysfs ABI compatibility, as noted previously in commit de2a3eaea552
> ("nvmem: sunxi_sid: Optimize register read-out method").
> 
> Fixes: 07ae4fde9efa ("nvmem: sunxi_sid: Add support for D1 variant")
> Signed-off-by: Samuel Holland <samuel@...lland.org>

On a D1-Nezha:
Tested-by: Heiko Stuebner <heiko@...ech.de>