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Pratyush Yadav d15638bf76 Revert "mtd: spi-nor: core: replace dummy buswidth from addr to data" 
This reverts commit 98d1fb94ce.

The commit uses data nbits instead of addr nbits for dummy phase. This
causes a regression for all boards where spi-tx-bus-width is smaller
than spi-rx-bus-width. It is a common pattern for boards to have
spi-tx-bus-width == 1 and spi-rx-bus-width > 1. The regression causes
all reads with a dummy phase to become unavailable for such boards,
leading to a usually slower 0-dummy-cycle read being selected.

Most controllers' supports_op hooks call spi_mem_default_supports_op().
In spi_mem_default_supports_op(), spi_mem_check_buswidth() is called to
check if the buswidths for the op can actually be supported by the
board's wiring. This wiring information comes from (among other things)
the spi-{tx,rx}-bus-width DT properties. Based on these properties,
SPI_TX_* or SPI_RX_* flags are set by of_spi_parse_dt().
spi_mem_check_buswidth() then uses these flags to make the decision
whether an op can be supported by the board's wiring (in a way,
indirectly checking against spi-{rx,tx}-bus-width).

Now the tricky bit here is that spi_mem_check_buswidth() does:

	if (op->dummy.nbytes &&
	    spi_check_buswidth_req(mem, op->dummy.buswidth, true))
		return false;

The true argument to spi_check_buswidth_req() means the op is treated as
a TX op. For a board that has say 1-bit TX and 4-bit RX, a 4-bit dummy
TX is considered as unsupported, and the op gets rejected.

The commit being reverted uses the data buswidth for dummy buswidth. So
for reads, the RX buswidth gets used for the dummy phase, uncovering
this issue. In reality, a dummy phase is neither RX nor TX. As the name
suggests, these are just dummy cycles that send or receive no data, and
thus don't really need to have any buswidth at all.

Ideally, dummy phases should not be checked against the board's wiring
capabilities at all, and should only be sanity-checked for having a sane
buswidth value. Since we are now at rc7 and such a change might
introduce many unexpected bugs, revert the commit for now. It can be
sent out later along with the spi_mem_check_buswidth() fix.

Fixes: 98d1fb94ce ("mtd: spi-nor: core: replace dummy buswidth from addr to data")
Reported-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Closes: https://lore.kernel.org/linux-mtd/3342163.44csPzL39Z@steina-w/
Tested-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Signed-off-by: Pratyush Yadav <pratyush@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
2025-01-15 18:44:23 +01:00
arch s390: 2025-01-12 12:04:53 -08:00
block block, bfq: fix waker_bfqq UAF after bfq_split_bfqq() 2025-01-09 06:52:46 -07:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: rsassa-pkcs1 - Copy source data for SG list 2024-12-10 13:34:05 +08:00
Documentation Char/Misc/IIO driver fixes for 6.13-rc7 2025-01-12 14:34:00 -08:00
drivers Revert "mtd: spi-nor: core: replace dummy buswidth from addr to data" 2025-01-15 18:44:23 +01:00
fs Driver core and debugfs fixes for 6.13-rc7 2025-01-12 14:26:31 -08:00
include s390: 2025-01-12 12:04:53 -08:00
init - The series "resource: A couple of cleanups" from Andy Shevchenko 2024-11-25 16:09:48 -08:00
io_uring io_uring-6.13-20250111 2025-01-11 10:59:43 -08:00
ipc - The series "resource: A couple of cleanups" from Andy Shevchenko 2024-11-25 16:09:48 -08:00
kernel - Fix a #GP in the perf user callchain code caused by a race between uprobe 2025-01-12 11:57:45 -08:00
lib maple_tree: reload mas before the second call for mas_empty_area 2024-12-30 17:59:07 -08:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm Revert "vmstat: disable vmstat_work on vmstat_cpu_down_prep()" 2025-01-06 06:10:24 -08:00
net netfilter pull request 25-01-09 2025-01-09 08:54:49 -08:00
rust workqueue: Fixes for v6.13-rc5 2025-01-03 15:03:56 -08:00
samples BPF fixes: 2024-12-06 15:07:48 -08:00
scripts Kbuild fixes for v6.13 (3rd) 2025-01-05 10:52:47 -08:00
security selinux/stable-6.13 PR 20250107 2025-01-07 14:49:48 -08:00
sound sound fixes for 6.13-rc6 2025-01-03 10:54:51 -08:00
tools s390: 2025-01-12 12:04:53 -08:00
usr kbuild: Drop support for include/asm-<arch> in headers_check.pl 2024-12-21 11:43:17 +09:00
virt VFIO updates for v6.13 2024-11-27 12:57:03 -08:00
.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.clippy.toml rust: enable Clippy's check-private-items 2024-10-07 21:39:57 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: Retire Ralf Baechle 2024-11-12 15:48:59 +01:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore Kbuild updates for v6.13 2024-11-30 13:41:50 -08:00
.mailmap Staging driver fixes for 6.13-rc7 2025-01-12 14:22:13 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: remove Andy Gospodarek from bonding 2025-01-09 08:30:01 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: powerpc: Update my status 2025-01-10 17:19:33 -08:00
Makefile Linux 6.13-rc7 2025-01-12 14:37:56 -08:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.