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Manivannan Sadhasivam 7799c9dd6d PCI: rockchip: Use GPIOD_OUT_LOW flag while requesting ep_gpio 
commit 840b7a5edf upstream.

Rockchip platforms use 'GPIO_ACTIVE_HIGH' flag in the devicetree definition
for ep_gpio. This means, whatever the logical value set by the driver for
the ep_gpio, physical line will output the same logic level.

For instance,

  gpiod_set_value_cansleep(rockchip->ep_gpio, 0); --> Level low
  gpiod_set_value_cansleep(rockchip->ep_gpio, 1); --> Level high

But while requesting the ep_gpio, GPIOD_OUT_HIGH flag is currently used.
Now, this also causes the physical line to output 'high' creating trouble
for endpoint devices during host reboot.

When host reboot happens, the ep_gpio will initially output 'low' due to
the GPIO getting reset to its POR value. Then during host controller probe,
it will output 'high' due to GPIOD_OUT_HIGH flag. Then during
rockchip_pcie_host_init_port(), it will first output 'low' and then 'high'
indicating the completion of controller initialization.

On the endpoint side, each output 'low' of ep_gpio is accounted for PERST#
assert and 'high' for PERST# deassert. With the above mentioned flow during
host reboot, endpoint will witness below state changes for PERST#:

  (1) PERST# assert - GPIO POR state
  (2) PERST# deassert - GPIOD_OUT_HIGH while requesting GPIO
  (3) PERST# assert - rockchip_pcie_host_init_port()
  (4) PERST# deassert - rockchip_pcie_host_init_port()

Now the time interval between (2) and (3) is very short as both happen
during the driver probe(), and this results in a race in the endpoint.
Because, before completing the PERST# deassertion in (2), endpoint got
another PERST# assert in (3).

A proper way to fix this issue is to change the GPIOD_OUT_HIGH flag in (2)
to GPIOD_OUT_LOW. Because the usual convention is to request the GPIO with
a state corresponding to its 'initial/default' value and let the driver
change the state of the GPIO when required.

As per that, the ep_gpio should be requested with GPIOD_OUT_LOW as it
corresponds to the POR value of '0' (PERST# assert in the endpoint). Then
the driver can change the state of the ep_gpio later in
rockchip_pcie_host_init_port() as per the initialization sequence.

This fixes the firmware crash issue in Qcom based modems connected to
Rockpro64 based board.

Fixes: e77f847df5 ("PCI: rockchip: Add Rockchip PCIe controller support")
Closes: https://lore.kernel.org/mhi/20240402045647.GG2933@thinkpad/
Link: https://lore.kernel.org/linux-pci/20240416-pci-rockchip-perst-fix-v1-1-4800b1d4d954@linaro.org
Reported-by: Slark Xiao <slark_xiao@163.com>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Niklas Cassel <cassel@kernel.org>
Cc: stable@vger.kernel.org	# v4.9
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2024-08-19 05:45:15 +02:00
arch KVM: VMX: Split out the non-virtualization part of vmx_interrupt_blocked() 2024-08-19 05:45:14 +02:00
block block: initialize integrity buffer to zero before writing it to media 2024-08-19 05:44:50 +02:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-22 14:22:01 +02:00
crypto crypto: aead,cipher - zeroize key buffer after use 2024-07-18 13:07:27 +02:00
Documentation dt-bindings: thermal: correct thermal zone node name limit 2024-08-19 05:45:10 +02:00
drivers PCI: rockchip: Use GPIOD_OUT_LOW flag while requesting ep_gpio 2024-08-19 05:45:15 +02:00
fs jbd2: make jbd2_journal_get_max_txn_bufs() internal 2024-08-19 05:45:14 +02:00
include jbd2: make jbd2_journal_get_max_txn_bufs() internal 2024-08-19 05:45:14 +02:00
init init/main.c: Fix potential static_command_line memory overflow 2024-04-27 17:05:28 +02:00
io_uring io_uring: tighten task exit cancellations 2024-08-19 05:45:14 +02:00
ipc ipc/sem: Fix dangling sem_array access in semtimedop race 2022-12-08 11:28:45 +01:00
kernel task_work: Introduce task_work_cancel() again 2024-08-19 05:45:13 +02:00
lib mlxsw: spectrum_acl_erp: Fix object nesting warning 2024-08-19 05:44:56 +02:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm mm: mmap_lock: replace get_memcg_path_buf() with on-stack buffer 2024-08-19 05:45:10 +02:00
net ipv6: take care of scope when choosing the src addr 2024-08-19 05:45:11 +02:00
samples Add gitignore file for samples/fanotify/ subdirectory 2024-07-27 10:46:16 +02:00
scripts kconfig: remove wrong expr_trans_bool() 2024-07-27 10:46:09 +02:00
security task_work: s/task_work_cancel()/task_work_cancel_func()/ 2024-08-19 05:45:13 +02:00
sound ALSA: usb-audio: Add a quirk for Sonix HD USB Camera 2024-08-19 05:45:15 +02:00
tools tools/memory-model: Fix bug in lock.cat 2024-08-19 05:45:15 +02:00
usr usr/include/Makefile: add linux/nfc.h to the compile-test coverage 2022-02-01 17:27:15 +01:00
virt KVM: Always flush async #PF workqueue when vCPU is being destroyed 2024-04-10 16:18:34 +02:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: add Andrej Shadura 2021-10-18 20:22:03 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS trace: Relocate event helper files 2024-04-10 16:19:24 +02:00
Makefile Linux 5.15.164 2024-07-27 10:46:18 +02:00
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.