4.19-stable review patch. If anyone has any objections, please let me know.
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From: Billy Tsai billy_tsai@aspeedtech.com
[ Upstream commit 1bb5a99e1f3fd27accb804aa0443a789161f843c ]
Performing a dummy read ensures that the register write operation is fully completed, mitigating any potential bus delays that could otherwise impact the frequency of bitbang usage. E.g., if the JTAG application uses GPIO to control the JTAG pins (TCK, TMS, TDI, TDO, and TRST), and the application sets the TCK clock to 1 MHz, the GPIO's high/low transitions will rely on a delay function to ensure the clock frequency does not exceed 1 MHz. However, this can lead to rapid toggling of the GPIO because the write operation is POSTed and does not wait for a bus acknowledgment.
Fixes: 361b79119a4b ("gpio: Add Aspeed driver") Reviewed-by: Andrew Jeffery andrew@codeconstruct.com.au Signed-off-by: Billy Tsai billy_tsai@aspeedtech.com Link: https://lore.kernel.org/r/20241008081450.1490955-2-billy_tsai@aspeedtech.com Signed-off-by: Bartosz Golaszewski bartosz.golaszewski@linaro.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/gpio/gpio-aspeed.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/drivers/gpio/gpio-aspeed.c b/drivers/gpio/gpio-aspeed.c index ba1cd971d50b6..5cc80678ac352 100644 --- a/drivers/gpio/gpio-aspeed.c +++ b/drivers/gpio/gpio-aspeed.c @@ -407,6 +407,8 @@ static void __aspeed_gpio_set(struct gpio_chip *gc, unsigned int offset, gpio->dcache[GPIO_BANK(offset)] = reg;
iowrite32(reg, addr); + /* Flush write */ + ioread32(addr); }
static void aspeed_gpio_set(struct gpio_chip *gc, unsigned int offset,