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

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Message-ID: <440be61d-b60e-4179-8481-b9a7a0dabae5@kernel.org>
Date: Sat, 7 Sep 2024 14:54:33 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Nick Chan <towinchenmi@...il.com>, Alim Akhtar <alim.akhtar@...sung.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Jiri Slaby <jirislaby@...nel.org>, linux-arm-kernel@...ts.infradead.org,
 linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-serial@...r.kernel.org
Cc: asahi@...ts.linux.dev
Subject: Re: [PATCH 1/2] tty: serial: samsung: Fix A7-A11 serial earlycon
 SError

On 07/09/2024 13:06, Nick Chan wrote:
> 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 <towinchenmi@...il.com>
> ---
>  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.



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

Best regards,
Krzysztof