mirror of
https://github.com/openwrt/openwrt.git
synced 2024-12-23 07:22:33 +00:00
8c405cdccc
The patches were generated from the RPi repo with the following command: git format-patch v6.6.34..rpi-6.1.y Some patches needed rebasing and, as usual, the applied and reverted, wireless drivers, Github workflows, READMEs and defconfigs patches were removed. Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
51 lines
1.7 KiB
Diff
51 lines
1.7 KiB
Diff
From a7c6699c4ddfe450cfef583f4f490bbafcfcff18 Mon Sep 17 00:00:00 2001
|
|
From: Phil Elwell <phil@raspberrypi.com>
|
|
Date: Thu, 28 Jan 2021 11:30:04 +0000
|
|
Subject: [PATCH 0276/1085] spi: bcm2835: Workaround/fix for zero-length
|
|
transfers
|
|
|
|
A relatively recent commit ([1]) contained optimisation for the PIO
|
|
SPI FIFO-filling functions. The commit message includes the phrase
|
|
"[t]he blind and counted loops are always called with nonzero count".
|
|
This is technically true, but it is still possible for count to become
|
|
zero before the loop is entered - if tfr->len is zero. Moving the loop
|
|
exit condition to the end of the loop saves a few cycles, but results
|
|
in a near-infinite loop should the revised count be zero on entry.
|
|
|
|
Strangely, zero-lengthed transfers aren't filtered by the SPI framework
|
|
and, even more strangely, the Python3 spidev library is triggering them
|
|
for no obvious reason.
|
|
|
|
Avoid the problem completely by bailing out of the main transfer
|
|
function early if trf->len is zero, although there may be a case for
|
|
moving the mitigation into the framework.
|
|
|
|
See: https://github.com/raspberrypi/linux/issues/4100
|
|
|
|
Signed-off-by: Phil Elwell <phil@raspberrypi.com>
|
|
|
|
[1] 26751de25d25 ("spi: bcm2835: Micro-optimise FIFO loops")
|
|
---
|
|
drivers/spi/spi-bcm2835.c | 10 ++++++++++
|
|
1 file changed, 10 insertions(+)
|
|
|
|
--- a/drivers/spi/spi-bcm2835.c
|
|
+++ b/drivers/spi/spi-bcm2835.c
|
|
@@ -1055,6 +1055,16 @@ static int bcm2835_spi_transfer_one(stru
|
|
unsigned long hz_per_byte, byte_limit;
|
|
u32 cs = target->prepare_cs;
|
|
|
|
+ if (unlikely(!tfr->len)) {
|
|
+ static int warned;
|
|
+
|
|
+ if (!warned)
|
|
+ dev_warn(&spi->dev,
|
|
+ "zero-length SPI transfer ignored\n");
|
|
+ warned = 1;
|
|
+ return 0;
|
|
+ }
|
|
+
|
|
/* set clock */
|
|
spi_hz = tfr->speed_hz;
|
|
|