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

[Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>]

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)


Best regards,
Krzysztof