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Ilpo Järvinen e736180eaf serial: 8250: Prevent starting up DMA Rx on THRI interrupt 
commit 90b8596ac4 upstream.

Hans de Goede reported Bluetooth adapters (HCIs) connected over an UART
connection failed due corrupted Rx payload. The problem was narrowed
down to DMA Rx starting on UART_IIR_THRI interrupt. The problem occurs
despite LSR having DR bit set, which is precondition for attempting to
start DMA Rx in the first place.

From a debug patch:
[x.807834] 8250irq: iir=cc lsr+saved=60 received=0/15 ier=0f dma_t/rx/err=0/0/0
[x.808676] 8250irq: iir=c2 lsr+saved=61 received=0/0 ier=0f dma_t/rx/err=0/0/0
[x.808776] 8250irq: iir=cc lsr+saved=60 received=1/12 ier=0d dma_t/rx/err=0/1/0
[x.808870] Bluetooth: hci0: Frame reassembly failed (-84)

In the debug snippet, received field indicates 1 byte was transferred
over DMA and 12 bytes after that with the non-DMA Rx. The sole byte DMA
handled was corrupted (gets zeroed) which leads to the HCI failure.

This problem became apparent after commit e8ffbb71f7 ("serial: 8250:
use THRE & __stop_tx also with DMA") changed Tx stop behavior. Tx stop
is now triggered from a THRI interrupt.

Despite that this problem looks like a HW bug, this fix is not adding
UART_BUG_xx flag to the driver beucase it seems useful in general to
avoid starting DMA when there are only a few bytes to transfer.
Skipping DMA for small transfers avoids the extra overhead DMA incurs.

Thus, don't setup DMA Rx on UART_IIR_THRI but leave it to a subsequent
interrupt which has Rx a related IIR value.

By returning false from handle_rx_dma(), the DMA vs non-DMA decision is
postponed until either UART_IIR_RDI (FIFO threshold worth of bytes
awaiting) or UART_IIR_TIMEOUT (inter-character timeout) triggers at a
later time which allows better to discern whether the number of bytes
warrants starting DMA or not.

Reported-by: Hans de Goede <hdegoede@redhat.com>
Tested-by: Hans de Goede <hdegoede@redhat.com>
Fixes: e8ffbb71f7 ("serial: 8250: use THRE & __stop_tx also with DMA")
Cc: stable@vger.kernel.org
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20230317103034.12881-1-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2023-04-13 16:55:28 +02:00
arch arm64: compat: Work around uninitialized variable warning 2023-04-13 16:55:24 +02:00
block block: do not reverse request order when flushing plug list 2023-03-22 13:33:46 +01:00
certs certs: Fix build error when PKCS#11 URI contains semicolon 2023-02-09 11:28:11 +01:00
crypto crypto: rsa-pkcs1pad - Use akcipher_request_complete 2023-03-10 09:33:03 +01:00
Documentation dt-bindings: serial: renesas,scif: Fix 4th IRQ for 4-IRQ SCIFs 2023-04-13 16:55:28 +02:00
drivers serial: 8250: Prevent starting up DMA Rx on THRI interrupt 2023-04-13 16:55:28 +02:00
fs nilfs2: fix sysfs interface lifetime 2023-04-13 16:55:28 +02:00
include cxl/pci: Fix CDAT retrieval on big endian 2023-04-13 16:55:24 +02:00
init gcc: disable -Warray-bounds for gcc-11 too 2023-01-14 10:33:43 +01:00
io_uring io_uring: fix poll/netmsg alloc caches 2023-04-06 12:10:52 +02:00
ipc ipc: fix memory leak in init_mqueue_fs() 2022-12-31 13:32:01 +01:00
kernel tracing: Fix wrong return in kprobe_event_gen_test.c 2023-04-06 12:10:41 +02:00
lib zstd: Fix definition of assert() 2023-04-06 12:10:38 +02:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm mm/ksm: fix race with VMA iteration and mm_struct teardown 2023-03-30 12:49:29 +02:00
net netlink: annotate lockless accesses to nlk->max_recvmsg_len 2023-04-13 16:55:24 +02:00
rust rust: print: avoid evaluating arguments in pr_* macros in unsafe blocks 2023-02-06 08:06:34 +01:00
samples ftrace: Export ftrace_free_filter() to modules 2023-02-01 08:34:37 +01:00
scripts modpost: Fix processing of CRCs on 32-bit build machines 2023-04-06 12:10:53 +02:00
security keys: Do not cache key in task struct if key is requested from kernel thread 2023-03-30 12:49:07 +02:00
sound ALSA: hda/hdmi: Preserve the previous PCM device upon re-enablement 2023-04-13 16:55:21 +02:00
tools libbpf: Fix btf_dump's packed struct determination 2023-04-06 12:10:58 +02:00
usr usr/gen_init_cpio.c: remove unnecessary -1 values from int file 2022-10-03 14:21:44 -07:00
virt KVM: Register /dev/kvm as the _very_ last thing during initialization 2023-03-10 09:34:11 +01:00
.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 Kbuild: add Rust support 2022-09-28 09:02:20 +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 audit: update the mailing list in MAINTAINERS 2023-02-25 11:25:42 +01:00
Makefile Linux 6.1.23 2023-04-06 12:10:58 +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.