Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Heiko =?ISO-8859-1?Q?St=FCbner?= <heiko@sntech.de>
To:     Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
        Chen-Yu Tsai <wens@csie.org>,
        Jernej Skrabec <jernej.skrabec@gmail.com>,
        linux-arm-kernel@lists.infradead.org
Cc:     Samuel Holland <samuel@sholland.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Rob Herring <robh+dt@kernel.org>, devicetree@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-sunxi@lists.linux.dev, Samuel Holland <samuel@sholland.org>
Subject: Re: [PATCH 1/4] nvmem: sunxi_sid: Always use 32-bit MMIO reads
Date:   Thu, 25 Aug 2022 14:05:08 +0200
Message-ID: <5410996.rnE6jSC6OK@diego>
In-Reply-To: <20220814173656.11856-2-samuel@sholland.org>
References: <20220814173656.11856-1-samuel@sholland.org> <20220814173656.11856-2-samuel@sholland.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 7Bit
Content-Type: text/plain; charset="us-ascii"
Precedence: bulk

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@sholland.org>

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