linux-kernel - [PATCH 02/10] nvmem: sunxi_sid: Always use 32-bit MMIO reads

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Message-Id: <20230127104015.23839-3-srinivas.kandagatla@linaro.org>
Date:   Fri, 27 Jan 2023 10:40:07 +0000
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     gregkh@...uxfoundation.org
Cc:     linux-kernel@...r.kernel.org, Samuel Holland <samuel@...lland.org>,
        stable@...r.kernel.org, Heiko Stuebner <heiko@...ech.de>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Subject: [PATCH 02/10] nvmem: sunxi_sid: Always use 32-bit MMIO reads

From: Samuel Holland <samuel@...lland.org>

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").

Cc: stable@...r.kernel.org
Fixes: 07ae4fde9efa ("nvmem: sunxi_sid: Add support for D1 variant")
Tested-by: Heiko Stuebner <heiko@...ech.de>
Signed-off-by: Samuel Holland <samuel@...lland.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@...aro.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;
 }
-- 
2.25.1