linux-kernel - [PATCH v2 0/7] spi: multi CS cleanup and controller CS limit removal

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Message-ID: <20250915183725.219473-1-jonas.gorski@gmail.com>
Date: Mon, 15 Sep 2025 20:37:18 +0200
From: Jonas Gorski <jonas.gorski@...il.com>
To: Mark Brown <broonie@...nel.org>,
	Amit Kumar Mahapatra <amit.kumar-mahapatra@....com>
Cc: linux-spi@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Marc Kleine-Budde <mkl@...gutronix.de>
Subject: [PATCH v2 0/7] spi: multi CS cleanup and controller CS limit removal

This series aims at cleaning up the current multi CS parts and removing
the CS limit per controller that was introduced with the multi CS
support.

To do this, store the assigned chip selects per device in
spi_device::num_chipselects, which allows us to use that instead of
SPI_CS_CNT_MAX for most loops, as well as remove the check for
SPI_INVALID_CS for any chip select.

This should hopefully make it obvious that SPI_CS_CNT_MAX only limits
accesses to arrays indexed by the number of chip selects of a device,
not the controller, and we can remove the check for
spi_controller::num_chipselects being less than SPI_CS_CNT_MAX in device
registration (which was the wrong place to do that anyway).

After having done that, we can reduce SPI_CS_CNT_MAX again to 4 without
breaking devices on higher CS lines.

Finally, rename SPI_CS_CNT_MAX to SPI_DEVICE_CNT_MAX to make it more
clear that this limit only applies to devices, not controllers.

There are still more issues left, but these can be addressed in future
submissions:

* The code allows multi-cs devices for any controller, as long as the
  device does not set parallel-memories.
* No current spi controller driver handles logical chip selects other
  than the first one, and always use it, regardless what cs_index_mask
  says.
* While most spi controllers should be able to handle devices that have
  multiple cs that just get enabled selectively, but not at the same
  time, there is no way to tell that to the core (ties into the above).
* There is no parallel memories/multi cs flag for devices, so any
  implementing driver needs to check the device tree node, making it
  impossible to register these kind of devices via platform code.

Changes v1 -> v2:

* rebased onto current spi/for-next
* kept the initialization of spi_device::chip_select[] to SPI_INVALID_CS
* reworded the reduce patch to not be a revert anymore

Jonas Gorski (7):
  spi: fix return code when spi device has too many chipselects
  spi: keep track of number of chipselects in spi_device
  spi: move unused device CS initialization to __spi_add_device()
  spi: drop check for validity of device chip selects
  spi: don't check spi_controller::num_chipselect when parsing a dt
    device
  spi: reduce device chip select limit again
  spi: rename SPI_CS_CNT_MAX => SPI_DEVICE_CS_CNT_MAX

 drivers/spi/spi-cadence-quadspi.c |  2 +-
 drivers/spi/spi.c                 | 75 +++++++++++++------------------
 include/linux/spi/spi.h           | 16 ++++---
 3 files changed, 42 insertions(+), 51 deletions(-)

base-commit: 34c2202f5ca2325511a0e0b8802492eec17a2c76
-- 
2.43.0