Re: [PATCH 06/12] tty: serial: samsung: Add Exynos850 SoC data

[Sam Protsenko <semen.protsenko@xxxxxxxxxx>]

On Fri, 30 Jul 2021 at 19:05, Krzysztof Kozlowski
<krzysztof.kozlowski@xxxxxxxxxxxxx> wrote:
>
> On 30/07/2021 16:49, Sam Protsenko wrote:
> > Add serial driver data for Exynos850 SoC. This driver data is basically
> > reusing EXYNOS_COMMON_SERIAL_DRV_DATA, which is common for all Exynos
> > chips, but also enables USI init, which was added in previous commit:
> > "tty: serial: samsung: Init USI to keep clocks running".
> >
> > Signed-off-by: Sam Protsenko <semen.protsenko@xxxxxxxxxx>
> > ---
> >  drivers/tty/serial/samsung_tty.c | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> >
> > diff --git a/drivers/tty/serial/samsung_tty.c b/drivers/tty/serial/samsung_tty.c
> > index 75ccbb08df4a..d059b516a0f4 100644
> > --- a/drivers/tty/serial/samsung_tty.c
> > +++ b/drivers/tty/serial/samsung_tty.c
> > @@ -2814,11 +2814,19 @@ static struct s3c24xx_serial_drv_data exynos5433_serial_drv_data = {
> >       .fifosize = { 64, 256, 16, 256 },
> >  };
> >
> > +static struct s3c24xx_serial_drv_data exynos850_serial_drv_data = {
> > +     EXYNOS_COMMON_SERIAL_DRV_DATA_USI(1),
> > +     .fifosize = { 0, },
>
> This does not look correct. You rely on samsung,uart-fifosize property
> but it is optional.
>

Good point. I will replace fifosize elements (in patch series v2) with
this code (the reasoning is below):

    .fifosize = { 256, 64, 64, 64 }

TRM mentions that USI block has configurable FIFO of 16/32/64/128/256
byte. In vendor kernel they are setting default values in dtsi instead
of driver, that's where fifosize = { 0 } appeared from. And in vendor
dtsi they set 256 for serial_0 (USI UART instance), 64 for serial_1
(CMGP0 UART instance) and 64 for serial_2 (CMGP1 UART instance). I
tested 256 and 64 for serial_0 (which is used for serial console)

As for fifosize array elements count: though it's possible to
configure up to 7 UARTs in Exynos850 (it has 5 USI blocks and 2 CMGP
blocks, which can be configured as USIs), in a regular case it's only
3 UARTs (1 in USI and 2 in CMGP). This is how it's done in vendor's
device tree, and I doubt someone is going to need more than 3 serials
anyway, looks like very specific case for a mobile SoC. But
CONFIG_SERIAL_SAMSUNG_UARTS_4=y is set by default when using arm64
defconfig, and I'd like to keep minimal delta for this defconfig for
now.

Hope you are ok with this?

Thanks!

>
> Best regards,
> Krzysztof