Linux-SPI Archive on lore.kernel.org
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From: Lukas Wunner <lukas@wunner.de>
To: Mark Brown <broonie@kernel.org>
Cc: "Nicolas Saenz Julienne" <nsaenzjulienne@suse.de>,
	Martin Sperl <kernel@martin.sperl.org>,
	linux-spi@vger.kernel.org, linux-rpi-kernel@lists.infradead.org
Subject: [PATCH 5/5] spi: Document devm_spi_register_controller() gotcha
Date: Fri, 15 May 2020 17:58:05 +0200
Message-ID: <d0dcbd098401b5d2a486eee7cf2f9dcabacf9605.1589557526.git.lukas@wunner.de> (raw)
In-Reply-To: <cover.1589557526.git.lukas@wunner.de>

As a rule, devm_spi_register_controller() must not be used if the
driver's ->remove() hook performs teardown steps which shall be
performed after unbinding of slaves.

Dozens of drivers are doing it wrong.  Document this gotcha to
hopefully prevent further misuse.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
---
 drivers/spi/spi.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index d32bdc6cbf66..e1a35aa7eeb8 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -2714,6 +2714,13 @@ static void devm_spi_unregister(struct device *dev, void *res)
  * Register a SPI device as with spi_register_controller() which will
  * automatically be unregistered and freed.
  *
+ * Be aware that a managed SPI controller and the attached slaves are
+ * unregistered after the driver's ->remove() callback has been executed.
+ * So the SPI slaves may still access the bus during and after ->remove().
+ * Thus, devm_spi_register_controller() may only be used if there is no
+ * ->remove() callback at all or if it does not perform teardown steps
+ * which render the bus inaccessible.
+ *
  * Return: zero on success, else a negative error code.
  */
 int devm_spi_register_controller(struct device *dev,
-- 
2.26.2


  parent reply index

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-15 15:58 [PATCH 0/5] Raspberry Pi SPI unbind fixes Lukas Wunner
2020-05-15 15:58 ` [PATCH 1/5] spi: Fix controller unregister order Lukas Wunner
2020-05-15 16:27   ` Mark Brown
2020-05-15 16:31     ` Lukas Wunner
2020-05-15 21:37       ` Andy Shevchenko
2020-05-16  6:45         ` Lukas Wunner
2020-05-16  9:45           ` Andy Shevchenko
2020-05-15 15:58 ` [PATCH 2/5] spi: bcm2835: " Lukas Wunner
2020-05-15 16:29   ` Mark Brown
2020-05-15 16:44     ` Lukas Wunner
2020-05-15 21:33       ` Andy Shevchenko
2020-05-16  6:56         ` Lukas Wunner
2020-05-16  9:40           ` Andy Shevchenko
2020-05-15 15:58 ` [PATCH 3/5] spi: bcm2835aux: " Lukas Wunner
2020-05-15 15:58 ` [PATCH 4/5] spi: bcm2835: Tear down DMA before turning off SPI controller Lukas Wunner
2020-05-15 15:58 ` Lukas Wunner [this message]
2020-05-15 16:30   ` [PATCH 5/5] spi: Document devm_spi_register_controller() gotcha Mark Brown
2020-05-20 17:17 ` [PATCH 0/5] Raspberry Pi SPI unbind fixes Mark Brown

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