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[34.125.100.95]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3b07c896cc6sm6096249a91.9.2026.11.03.14.53.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 03 Nov 2026 14:53:34 -0800 (PST) From: Joseph CT Chan To: Mark Brown Cc: linux-spi@vger.kernel.org, David Lechner , Bart Van Assche , Joseph CT Chan , stable@vger.kernel.org Subject: [PATCH v2 2/5] spi: spi-mux: re-apply settings after child calls spi_setup() Date: Tue, 3 Nov 2026 22:53:05 +0000 Message-ID: <20261103225308.3633046-3-jctchan@gmail.com> X-Mailer: git-send-email 2.56.0.385.gac671c819a-goog In-Reply-To: <20261103225308.3633046-1-jctchan@gmail.com> References: <20261103225308.3633046-1-jctchan@gmail.com> X-Mailing-List: linux-spi@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Joseph CT Chan spi_mux_select() copies a child's max_speed_hz, mode and bits_per_word into the spi-mux device and sets up the parent controller only when the mux switches to a different child (current_cs differs). If the child that is already selected changes its settings and calls spi_setup(), spi_mux_setup() only calls spi_setup() on the spi-mux device with its old settings, and current_cs still matches. The next transfers of that child then run with the old speed and mode. Set current_cs to SPI_MUX_NO_CS in spi_mux_setup(), so the next transfer copies the child's settings and sets up the parent again. spi_mux_setup() runs under the spi-mux controller's io_mutex, which the message pump holds while a message is forwarded, so this does not race with spi_mux_select(). The cost is one extra parent spi_setup() on the next transfer. Tested with KUnit (spi_mux: spi_mux_settings_lifecycle_test, added later in this series) on ARCH=um; builds with W=1 on x86_64. Not tested on hardware. Developed with help from the Claude and Gemini AI assistants. Fixes: e9e40543ad5b ("spi: Add generic SPI multiplexer") Cc: stable@vger.kernel.org Signed-off-by: Joseph CT Chan --- drivers/spi/spi-mux.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/spi/spi-mux.c b/drivers/spi/spi-mux.c index 28d7718138a5..a7ea6585b374 100644 --- a/drivers/spi/spi-mux.c +++ b/drivers/spi/spi-mux.c @@ -86,7 +86,13 @@ static int spi_mux_setup(struct spi_device *spi) * can be called multiple times, won't do a valid setup now but we will * change the settings when we do a transfer (necessary because we * can't predict from which device it will be anyway) + * + * The child may have changed its settings, so make the next transfer + * copy them again even if this child is the current one. This runs + * under our io_mutex, so no message is being forwarded right now. */ + priv->current_cs = SPI_MUX_NO_CS; + return spi_setup(priv->spi); } -- 2.56.0.385.gac671c819a-goog