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![Mark Brown](/assets/img/avatar_default.png)
The spi-mux driver is rather too clever and attempts to resubmit any
message that is submitted to it to the parent controller with some
adjusted callbacks. This does not play at all nicely with the fast
path which now sets flags on the message indicating that it's being
handled through the fast path, we see async messages flagged as being on
the fast path. Ideally the spi-mux code would duplicate the message but
that's rather invasive and a bit fragile in that it relies on the mux
knowing which fields in the message to copy. Instead teach the core
that there are controllers which can't cope with the fast path and have
the mux flag itself as being such a controller, ensuring that messages
going via the mux don't get partially handled via the fast path.
This will reduce the performance of any spi-mux connected device since
we'll now always use the thread for both the actual controller and the
mux controller instead of just the actual controller but given that we
were always hitting the slow path anyway it's hopefully not too much of
an additional cost and it allows us to keep the fast path.
Fixes: ae7d2346dc
("spi: Don't use the message queue if possible in spi_sync")
Reported-by: Casper Andersson <casper.casan@gmail.com>
Tested-by: Casper Andersson <casper.casan@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20220901120732.49245-1-broonie@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>
202 lines
5.2 KiB
C
202 lines
5.2 KiB
C
// SPDX-License-Identifier: GPL-2.0
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//
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// General Purpose SPI multiplexer
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#include <linux/err.h>
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/mux/consumer.h>
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#include <linux/slab.h>
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#include <linux/spi/spi.h>
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#define SPI_MUX_NO_CS ((unsigned int)-1)
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/**
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* DOC: Driver description
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*
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* This driver supports a MUX on an SPI bus. This can be useful when you need
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* more chip selects than the hardware peripherals support, or than are
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* available in a particular board setup.
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*
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* The driver will create an additional SPI controller. Devices added under the
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* mux will be handled as 'chip selects' on this controller.
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*/
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/**
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* struct spi_mux_priv - the basic spi_mux structure
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* @spi: pointer to the device struct attached to the parent
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* spi controller
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* @current_cs: The current chip select set in the mux
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* @child_msg_complete: The mux replaces the complete callback in the child's
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* message to its own callback; this field is used by the
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* driver to store the child's callback during a transfer
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* @child_msg_context: Used to store the child's context to the callback
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* @child_msg_dev: Used to store the spi_device pointer to the child
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* @mux: mux_control structure used to provide chip selects for
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* downstream spi devices
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*/
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struct spi_mux_priv {
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struct spi_device *spi;
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unsigned int current_cs;
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void (*child_msg_complete)(void *context);
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void *child_msg_context;
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struct spi_device *child_msg_dev;
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struct mux_control *mux;
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};
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/* should not get called when the parent controller is doing a transfer */
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static int spi_mux_select(struct spi_device *spi)
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{
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struct spi_mux_priv *priv = spi_controller_get_devdata(spi->controller);
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int ret;
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ret = mux_control_select(priv->mux, spi->chip_select);
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if (ret)
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return ret;
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if (priv->current_cs == spi->chip_select)
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return 0;
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dev_dbg(&priv->spi->dev, "setting up the mux for cs %d\n",
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spi->chip_select);
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/* copy the child device's settings except for the cs */
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priv->spi->max_speed_hz = spi->max_speed_hz;
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priv->spi->mode = spi->mode;
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priv->spi->bits_per_word = spi->bits_per_word;
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priv->current_cs = spi->chip_select;
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return 0;
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}
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static int spi_mux_setup(struct spi_device *spi)
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{
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struct spi_mux_priv *priv = spi_controller_get_devdata(spi->controller);
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/*
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* can be called multiple times, won't do a valid setup now but we will
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* change the settings when we do a transfer (necessary because we
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* can't predict from which device it will be anyway)
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*/
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return spi_setup(priv->spi);
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}
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static void spi_mux_complete_cb(void *context)
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{
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struct spi_mux_priv *priv = (struct spi_mux_priv *)context;
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struct spi_controller *ctlr = spi_get_drvdata(priv->spi);
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struct spi_message *m = ctlr->cur_msg;
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m->complete = priv->child_msg_complete;
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m->context = priv->child_msg_context;
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m->spi = priv->child_msg_dev;
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spi_finalize_current_message(ctlr);
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mux_control_deselect(priv->mux);
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}
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static int spi_mux_transfer_one_message(struct spi_controller *ctlr,
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struct spi_message *m)
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{
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struct spi_mux_priv *priv = spi_controller_get_devdata(ctlr);
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struct spi_device *spi = m->spi;
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int ret;
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ret = spi_mux_select(spi);
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if (ret)
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return ret;
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/*
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* Replace the complete callback, context and spi_device with our own
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* pointers. Save originals
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*/
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priv->child_msg_complete = m->complete;
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priv->child_msg_context = m->context;
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priv->child_msg_dev = m->spi;
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m->complete = spi_mux_complete_cb;
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m->context = priv;
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m->spi = priv->spi;
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/* do the transfer */
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return spi_async(priv->spi, m);
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}
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static int spi_mux_probe(struct spi_device *spi)
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{
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struct spi_controller *ctlr;
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struct spi_mux_priv *priv;
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int ret;
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ctlr = spi_alloc_master(&spi->dev, sizeof(*priv));
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if (!ctlr)
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return -ENOMEM;
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spi_set_drvdata(spi, ctlr);
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priv = spi_controller_get_devdata(ctlr);
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priv->spi = spi;
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/*
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* Increase lockdep class as these lock are taken while the parent bus
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* already holds their instance's lock.
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*/
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lockdep_set_subclass(&ctlr->io_mutex, 1);
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lockdep_set_subclass(&ctlr->add_lock, 1);
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priv->mux = devm_mux_control_get(&spi->dev, NULL);
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if (IS_ERR(priv->mux)) {
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ret = dev_err_probe(&spi->dev, PTR_ERR(priv->mux),
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"failed to get control-mux\n");
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goto err_put_ctlr;
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}
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priv->current_cs = SPI_MUX_NO_CS;
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/* supported modes are the same as our parent's */
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ctlr->mode_bits = spi->controller->mode_bits;
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ctlr->flags = spi->controller->flags;
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ctlr->transfer_one_message = spi_mux_transfer_one_message;
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ctlr->setup = spi_mux_setup;
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ctlr->num_chipselect = mux_control_states(priv->mux);
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ctlr->bus_num = -1;
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ctlr->dev.of_node = spi->dev.of_node;
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ctlr->must_async = true;
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ret = devm_spi_register_controller(&spi->dev, ctlr);
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if (ret)
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goto err_put_ctlr;
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return 0;
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err_put_ctlr:
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spi_controller_put(ctlr);
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return ret;
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}
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static const struct spi_device_id spi_mux_id[] = {
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{ "spi-mux" },
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{ }
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};
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MODULE_DEVICE_TABLE(spi, spi_mux_id);
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static const struct of_device_id spi_mux_of_match[] = {
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{ .compatible = "spi-mux" },
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{ }
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};
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MODULE_DEVICE_TABLE(of, spi_mux_of_match);
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static struct spi_driver spi_mux_driver = {
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.probe = spi_mux_probe,
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.driver = {
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.name = "spi-mux",
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.of_match_table = spi_mux_of_match,
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},
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.id_table = spi_mux_id,
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};
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module_spi_driver(spi_mux_driver);
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MODULE_DESCRIPTION("SPI multiplexer");
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MODULE_LICENSE("GPL");
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