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

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Date:   Sun, 14 Aug 2022 12:36:52 -0500
From:   Samuel Holland <samuel@...lland.org>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>
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
Subject: [PATCH 1/4] nvmem: sunxi_sid: Always use 32-bit MMIO reads

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>
---

 drivers/nvmem/sunxi_sid.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/nvmem/sunxi_sid.c b/drivers/nvmem/sunxi_sid.c
index 5750e1f4bcdb..92dfe4cb10e3 100644
--- a/drivers/nvmem/sunxi_sid.c
+++ b/drivers/nvmem/sunxi_sid.c
@@ -41,8 +41,21 @@ static int sunxi_sid_read(void *context, unsigned int offset,
 			  void *val, size_t bytes)
 {
 	struct sunxi_sid *sid = context;
+	u32 word;
+
+	/* .stride = 4 so offset is guaranteed to be aligned */
+	__ioread32_copy(val, sid->base + sid->value_offset + offset, bytes / 4);
 
-	memcpy_fromio(val, sid->base + sid->value_offset + offset, bytes);
+	val += round_down(bytes, 4);
+	offset += round_down(bytes, 4);
+	bytes = bytes % 4;
+
+	if (!bytes)
+		return 0;
+
+	/* Handle any trailing bytes */
+	word = readl_relaxed(sid->base + sid->value_offset + offset);
+	memcpy(val, &word, bytes);
 
 	return 0;
 }
-- 
2.35.1