Re: [PATCH 1/2] tty: serial: samsung: Fix A7-A11 serial earlycon SError

On 7/9/2024 20:54, Krzysztof Kozlowski wrote:

On 07/09/2024 13:06, Nick Chan wrote:

quoted

Apple's earlier SoCs, like A7-A11, requires 32-bit writes for the serial
port. Otherwise, a SError happens when writing to UTXH (+0x20). This only
manifested in earlycon as reg-io-width in the device tree is consulted
for normal serial writes.

Change the iotype of the port to UPIO_MEM32, to allow the serial port to
function on A7-A11 SoCs. This change does not appear to affect Apple M1 and
above.

Signed-off-by: Nick Chan <redacted>
---
 drivers/tty/serial/samsung_tty.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/samsung_tty.c b/drivers/tty/serial/samsung_tty.c
index c4f2ac9518aa..27b8a50bd3e7 100644
--- a/drivers/tty/serial/samsung_tty.c
+++ b/drivers/tty/serial/samsung_tty.c

@@ -2536,7 +2536,7 @@ static const struct s3c24xx_serial_drv_data s5l_serial_drv_data = {
 		.name		= "Apple S5L UART",
 		.type		= TYPE_APPLE_S5L,
 		.port_type	= PORT_8250,
-		.iotype		= UPIO_MEM,
+		.iotype		= UPIO_MEM32,
 		.fifosize	= 16,
 		.rx_fifomask	= S3C2410_UFSTAT_RXMASK,
 		.rx_fifoshift	= S3C2410_UFSTAT_RXSHIFT,

@@ -2825,8 +2825,10 @@ static int __init apple_s5l_early_console_setup(struct earlycon_device *device,
 	/* Close enough to S3C2410 for earlycon... */
 	device->port.private_data = &s3c2410_early_console_data;
 
+	/* ... however, we need to change the port iotype */
+	device->port.iotype = UPIO_MEM32;

If there is going to be resend, then this comment is redundant and can
be dropped - repeats the code and does not provide any explanation why.

Which would also make the patch smaller and easier to read. See GS101
earlycon.

I agree that the comment is quite useless as-is. However, I think it is
worthwhile to mention that A7-A11 expect MMIO32 register accesses here,
as someone looking at this code is likely using one of the newer SoCs,
which does not have this restriction.

Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>

Best regards,
Krzysztof

Nick Chan