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| author | Sam Protsenko <semen.protsenko@linaro.org> | 2021-08-11 14:48:24 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-08-13 10:14:36 +0300 |
| commit | 920792aa44ffb255c66d5295d71cc747d038cc98 (patch) | |
| tree | bddb7e98ffe5f7fa47b125bee2b3384069f7d8cd /include/linux/serial_s3c.h | |
| parent | 541b84eceef116a215e7c0d8bf1d35020bd4eafb (diff) | |
| download | linux-920792aa44ffb255c66d5295d71cc747d038cc98.tar.xz | |
tty: serial: samsung: Init USI to keep clocks running
UART block is a part of USI (Universal Serial Interface) IP-core in
Samsung SoCs since Exynos9810 (e.g. in Exynos850). USI allows one to
enable one of three types of serial interface: UART, SPI or I2C. That's
possible because USI shares almost all internal circuits within each
protocol. USI also provides some additional registers so it's possible
to configure it.
One USI register called USI_OPTION has reset value of 0x0. Because of
this the clock gating behavior is controlled by hardware (HWACG =
Hardware Auto Clock Gating), which simply means the serial won't work
after reset as is. In order to make it work, USI_OPTION[2:1] bits must
be set to 0b01, so that HWACG is controlled manually (by software).
Bits meaning:
- CLKREQ_ON = 1: clock is continuously provided to IP
- CLKSTOP_ON = 0: drive IP_CLKREQ to High (needs to be set along with
CLKREQ_ON = 1)
USI is not present on older chips, like s3c2410, s3c2412, s3c2440,
s3c6400, s5pv210, exynos5433, exynos4210. So the new boolean field
'.has_usi' was added to struct s3c24xx_uart_info. USI registers will be
only actually accessed when '.has_usi' field is set to "1".
This feature is needed for further serial enablement on Exynos850, but
some other new Exynos chips (like Exynos9810) may benefit from this
feature as well.
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Link: https://lore.kernel.org/r/20210811114827.27322-5-semen.protsenko@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'include/linux/serial_s3c.h')
| -rw-r--r-- | include/linux/serial_s3c.h | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/include/linux/serial_s3c.h b/include/linux/serial_s3c.h index f6c3323fc4c5..cf0de4a86640 100644 --- a/include/linux/serial_s3c.h +++ b/include/linux/serial_s3c.h @@ -27,6 +27,15 @@ #define S3C2410_UERSTAT (0x14) #define S3C2410_UFSTAT (0x18) #define S3C2410_UMSTAT (0x1C) +#define USI_CON (0xC4) +#define USI_OPTION (0xC8) + +#define USI_CON_RESET (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) #define S3C2410_LCON_CFGMASK ((0xF<<3)|(0x3)) |