linux-kernel - [PATCH] spi: stm32: drop devres version of spi_register

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Message-ID: <1615545286-5395-1-git-send-email-alain.volmat@foss.st.com>
Date:   Fri, 12 Mar 2021 11:34:46 +0100
From:   Alain Volmat <alain.volmat@...s.st.com>
To:     <broonie@...nel.org>, <amelie.delaunay@...s.st.com>
CC:     <mcoquelin.stm32@...il.com>, <alexandre.torgue@...s.st.com>,
        <linux-spi@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <fabrice.gasnier@...s.st.com>,
        <alain.volmat@...s.st.com>, <antonio.borneo@...s.st.com>
Subject: [PATCH] spi: stm32: drop devres version of spi_register_master

From: Antonio Borneo <antonio.borneo@...s.st.com>

A call to spi_unregister_master() triggers calling remove()
for all the spi devices binded to the spi master.

Some spi device driver requires to "talk" with the spi device
during the remove(), e.g.:
- a LCD panel like drivers/gpu/drm/panel/panel-lg-lg4573.c
  will turn off the backlighting sending a command over spi.
This implies that the spi master must be fully functional when
spi_unregister_master() is called, either if it is called
explicitly in the master's remove() code or implicitly by the
devres framework.

Devres calls devres_release_all() to release all the resources
"after" the remove() of the spi master driver (check code of
__device_release_driver() in drivers/base/dd.c).
If the spi master driver has an empty remove() then there would
be no issue; the devres_release_all() will release everything
in reverse order w.r.t. probe().
But if code in spi master driver remove() disables the spi or
makes it not functional (like in this spi-stm32), then devres
cannot be used safely for unregistering the spi master and the
binded spi devices.

Replace devm_spi_register_master() with spi_register_master()
and add spi_unregister_master() as first action in remove().

Fixes: dcbe0d84dfa5 ("spi: add driver for STM32 SPI controller")

Signed-off-by: Antonio Borneo <antonio.borneo@...s.st.com>
Signed-off-by: Alain Volmat <alain.volmat@...s.st.com>
---
 drivers/spi/spi-stm32.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi-stm32.c b/drivers/spi/spi-stm32.c
index 25c076461011..97cf3a2d4180 100644
--- a/drivers/spi/spi-stm32.c
+++ b/drivers/spi/spi-stm32.c
@@ -1929,7 +1929,7 @@ static int stm32_spi_probe(struct platform_device *pdev)
 	pm_runtime_set_active(&pdev->dev);
 	pm_runtime_enable(&pdev->dev);
 
-	ret = devm_spi_register_master(&pdev->dev, master);
+	ret = spi_register_master(master);
 	if (ret) {
 		dev_err(&pdev->dev, "spi master registration failed: %d\n",
 			ret);
@@ -1960,6 +1960,7 @@ static int stm32_spi_remove(struct platform_device *pdev)
 	struct spi_master *master = platform_get_drvdata(pdev);
 	struct stm32_spi *spi = spi_master_get_devdata(master);
 
+	spi_unregister_master(master);
 	spi->cfg->disable(spi);
 
 	if (master->dma_tx)
-- 
2.17.1