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From: =?utf-8?q?Th=C3=A9o_Lebrun?= <theo.lebrun@bootlin.com>
Date: Fri, 05 Apr 2024 17:02:16 +0200
Subject: [PATCH v2 06/11] spi: cadence-qspi: minimise register accesses on
 each op if !DTR
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Message-Id: <20240405-cdns-qspi-mbly-v2-6-956679866d6d@bootlin.com>
References: <20240405-cdns-qspi-mbly-v2-0-956679866d6d@bootlin.com>
In-Reply-To: <20240405-cdns-qspi-mbly-v2-0-956679866d6d@bootlin.com>
To: Mark Brown <broonie@kernel.org>, Rob Herring <robh+dt@kernel.org>, 
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>, 
 Conor Dooley <conor+dt@kernel.org>, Vaishnav Achath <vaishnav.a@ti.com>, 
 Thomas Bogendoerfer <tsbogend@alpha.franken.de>, 
 Rob Herring <robh@kernel.org>
Cc: linux-spi@vger.kernel.org, devicetree@vger.kernel.org, 
 linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org, 
 Vladimir Kondratiev <vladimir.kondratiev@mobileye.com>, 
 Gregory CLEMENT <gregory.clement@bootlin.com>, 
 Thomas Petazzoni <thomas.petazzoni@bootlin.com>, 
 Tawfik Bayouk <tawfik.bayouk@mobileye.com>, 
 =?utf-8?q?Th=C3=A9o_Lebrun?= <theo.lebrun@bootlin.com>

cqspi_enable_dtr() is called for each operation, commands or not, reads
or writes. It writes CQSPI_REG_CONFIG then waits for idle (three
successful reads). Skip that in the no-DTR case if DTR is already
disabled.

It cannot be skipped in the DTR case as cqspi_setup_opcode_ext() writes
to a register and we must wait for idle state.

According to ftrace, the average cqspi_exec_mem_op() call goes from
85.4µs to 83.6µs when reading 235M over UBIFS on an octal flash.

Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
---
 drivers/spi/spi-cadence-quadspi.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/spi/spi-cadence-quadspi.c b/drivers/spi/spi-cadence-quadspi.c
index 04a473fafe43..55d20d565fe5 100644
--- a/drivers/spi/spi-cadence-quadspi.c
+++ b/drivers/spi/spi-cadence-quadspi.c
@@ -492,8 +492,11 @@ static int cqspi_enable_dtr(struct cqspi_flash_pdata *f_pdata,
 		if (ret)
 			return ret;
 	} else {
-		reg &= ~CQSPI_REG_CONFIG_DTR_PROTO;
-		reg &= ~CQSPI_REG_CONFIG_DUAL_OPCODE;
+		unsigned int mask = CQSPI_REG_CONFIG_DTR_PROTO | CQSPI_REG_CONFIG_DUAL_OPCODE;
+		/* Shortcut if DTR is already disabled. */
+		if ((reg & mask) == 0)
+			return 0;
+		reg &= ~mask;
 	}
 
 	writel(reg, reg_base + CQSPI_REG_CONFIG);

-- 
2.44.0