linux-kernel - [PATCH 2/4] spi: cadence-qspi: set maximum chip-select to 4

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Date: Fri, 09 Feb 2024 14:45:31 +0100
From: Théo Lebrun <theo.lebrun@...tlin.com>
To: Mark Brown <broonie@...nel.org>
Cc: linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Dhruva Gole <d-gole@...com>, Gregory CLEMENT <gregory.clement@...tlin.com>, 
 Vladimir Kondratiev <vladimir.kondratiev@...ileye.com>, 
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
 Tawfik Bayouk <tawfik.bayouk@...ileye.com>, 
 Théo Lebrun <theo.lebrun@...tlin.com>
Subject: [PATCH 2/4] spi: cadence-qspi: set maximum chip-select to 4

Change the maximum chip-select count in cadence-qspi to 4 instead of 16.
The value gets used as default ->num_chipselect when the num-cs DT
property isn't received from devicetree. It also determines the
cqspi->f_pdata array size.

Hardware only supports values up to 4; see cqspi_chipselect() that sets
CS using a one-bit-per-CS 4-bit register field.

Add a static_assert() call as a defensive measure to ensure we stay
under the SPI subsystem limit. It got set to 4 when introduced in
4d8ff6b0991d ("spi: Add multi-cs memories support in SPI core") and
later increased to 16 in 2f8c7c3715f2 ("spi: Raise limit on number of
chip selects").

Signed-off-by: Théo Lebrun <theo.lebrun@...tlin.com>
---
 drivers/spi/spi-cadence-quadspi.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi-cadence-quadspi.c b/drivers/spi/spi-cadence-quadspi.c
index 7ba4d5d16fd2..e9e3abd2142c 100644
--- a/drivers/spi/spi-cadence-quadspi.c
+++ b/drivers/spi/spi-cadence-quadspi.c
@@ -31,7 +31,9 @@
 #include <linux/timer.h>

 #define CQSPI_NAME			"cadence-qspi"
-#define CQSPI_MAX_CHIPSELECT		16
+#define CQSPI_MAX_CHIPSELECT		4
+
+static_assert(CQSPI_MAX_CHIPSELECT <= SPI_CS_CNT_MAX);

 /* Quirks */
 #define CQSPI_NEEDS_WR_DELAY		BIT(0)

-- 
2.43.0