[PATCH 04/12] tty: serial: samsung: Init USI to keep clocks running

[Sam Protsenko]

On Tue, 3 Aug 2021 at 10:37, Krzysztof Kozlowski
<krzysztof.kozlowski at canonical.com> wrote:
>
> On 03/08/2021 01:06, Sam Protsenko wrote:
>
> (...)
>
> >>> diff --git a/include/linux/serial_s3c.h b/include/linux/serial_s3c.h
> >>> index f6c3323fc4c5..013c2646863e 100644
> >>> --- a/include/linux/serial_s3c.h
> >>> +++ b/include/linux/serial_s3c.h
> >>> @@ -28,6 +28,15 @@
> >>>  #define S3C2410_UFSTAT         (0x18)
> >>>  #define S3C2410_UMSTAT         (0x1C)
> >>>
> >>> +/* USI Control Register offset */
> >>> +#define USI_CON                      (0xC4)
> >>> +/* USI Option Register offset */
> >>> +#define USI_OPTION           (0xC8)
> >>> +/* USI_CON[0] = 0b0: clear USI global software reset (Active High) */
> >>> +#define USI_RESET            (0<<0)
> >>
> >> Just 0x0. I understand you wanted to hint it is a bit field, but the
> >> shift of 0 actually creates more questions.
> >>
> >
> > After some consideration I decided to adhere to existing style and do
> > something like this (in v2):
> >
> > 8<--------------------------------------------------------------------->8
> > #define USI_CON          (0xC4)
> > #define USI_OPTION      (0xC8)
> >
> > #define USI_CON_RESET_CLEAR        (0<<0)
> > #define USI_CON_RESET_SET        (1<<0)
> > #define USI_CON_RESET_MASK        (1<<0)
> >
> > #define USI_OPTION_HWACG_CLKREQ_ON    (1<<1)
> > #define USI_OPTION_HWACG_CLKSTOP_ON    (1<<2)
> > #define USI_OPTION_HWACG_MASK        (3<<1)
> > 8<--------------------------------------------------------------------->8
> >
> > The whole reason for those comments was missing public TRM. But in the
> > end I decided it just looks ugly. Also, this way I can do RMW
> > operation (discussed above) in more logical way.
> >
> > Please let me know if code snippets above look good to you.
>
> Please skip the USI_CON_RESET_CLEAR. There is no such pattern in the
> code. Clearing bit is an obvious operation and such code is already
> everywhere:
>     val &= ~USI_CON_RESET
>
> (or &= ~USI_RESET_MASK)
>
> Therefore for USI_CON_RESET only:
>     #define USI_CON_RESET             (1<<0)
>     #define USI_CON_RESET_MASK        (1<<0)
>

Sure, I'll make it so.

>
> Best regards,
> Krzysztof