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Pratyush Yadav 4c833c3652 Revert "mtd: spi-nor: core: replace dummy buswidth from addr to data" 
[ Upstream commit d15638bf76 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2025-01-23 17:17:11 +01:00
arch arm64: dts: rockchip: add hevc power domain clock to rk3328 2025-01-17 13:34:47 +01:00
block block, bfq: fix waker_bfqq UAF after bfq_split_bfqq() 2025-01-17 13:34:47 +01:00
certs certs: Fix build error when PKCS#11 URI contains semicolon 2023-02-09 11:28:11 +01:00
crypto crypto: api - Add crypto_clone_tfm 2024-12-14 19:53:51 +01:00
Documentation dt-bindings: display: adi,adv7533: Drop single lane support 2025-01-09 13:30:06 +01:00
drivers Revert "mtd: spi-nor: core: replace dummy buswidth from addr to data" 2025-01-23 17:17:11 +01:00
fs ocfs2: fix slab-use-after-free due to dangling pointer dqi_priv 2025-01-17 13:34:48 +01:00
include net: add exit_batch_rtnl() method 2025-01-23 17:17:09 +01:00
init initramfs: avoid filename buffer overrun 2024-12-14 19:53:14 +01:00
io_uring io_uring/eventfd: ensure io_eventfd_signal() defers another RCU period 2025-01-17 13:34:47 +01:00
ipc ipc: fix memleak if msg_init_ns failed in create_ipc_ns 2024-12-14 19:54:06 +01:00
kernel bpf: Fix overloading of MEM_UNINIT's meaning 2025-01-17 13:34:43 +01:00
lib lib: stackinit: hide never-taken branch from compiler 2024-12-14 19:54:37 +01:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm mm: vmscan: account for free pages to prevent infinite Loop in throttle_direct_reclaim() 2025-01-09 13:30:07 +01:00
net net: add exit_batch_rtnl() method 2025-01-23 17:17:09 +01:00
rust rust: macros: provide correct provenance when constructing THIS_MODULE 2024-10-17 15:22:24 +02:00
samples samples/bpf: Fix a resource leak 2024-12-14 19:54:40 +01:00
scripts scripts/sorttable: fix orc_sort_cmp() to maintain symmetry and transitivity 2025-01-17 13:34:38 +01:00
security selinux: ignore unknown extended permissions 2025-01-09 13:29:56 +01:00
sound ASoC: mediatek: disable buffer pre-allocation 2025-01-17 13:34:38 +01:00
tools stddef: make __struct_group() UAPI C++-friendly 2025-01-02 10:30:51 +01:00
usr usr/gen_init_cpio.c: remove unnecessary -1 values from int file 2022-10-03 14:21:44 -07:00
virt KVM: Fix a data race on last_boosted_vcpu in kvm_vcpu_on_spin() 2024-06-27 13:46:21 +02:00
.clang-format inet: ping: use hlist_nulls rcu iterator during lookup 2022-12-01 12:42:46 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore Remove *.orig pattern from .gitignore 2024-10-17 15:21:15 +02:00
.mailmap 9 hotfixes. 6 for MM, 3 for other areas. Four of these patches address 2022-12-10 17:10:52 -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 Michal Marek from Kbuild maintainers 2022-11-16 14:53:00 +09:00
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: add leah to 6.1 MAINTAINERS file 2024-05-17 11:56:16 +02:00
Makefile Linux 6.1.126 2025-01-19 09:01:16 +01:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -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 Restructured Text 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.