gpio: aspeed: Add the flush write to ensure the write complete.

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[ Upstream commit 1bb5a99e1f ]

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: 361b79119a ("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>

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Billy Tsai 2024-10-08 16:14:44 +08:00 • committed by Greg Kroah-Hartman

parent cfa836da7f

commit 2a165df9ce

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drivers/gpio/gpio-aspeed.c

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