On 7/9/2024 20:54, Krzysztof Kozlowski wrote:
> 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@xxxxxxxxx>
>> ---
>> 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@xxxxxxxxxx>
>
> Best regards,
> Krzysztof
>
Nick Chan
