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From: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
To: "Sam Protsenko" <semen.protsenko@linaro.org>,
	"Sylwester Nawrocki" <s.nawrocki@samsung.com>,
	"Chanwoo Choi" <cw00.choi@samsung.com>,
	"Linus Walleij" <linus.walleij@linaro.org>,
	"Tomasz Figa" <tomasz.figa@gmail.com>,
	"Paweł Chmiel" <pawel.mikolaj.chmiel@gmail.com>
Cc: Marc Zyngier <maz@kernel.org>, Rob Herring <robh+dt@kernel.org>,
	Stephen Boyd <sboyd@kernel.org>,
	Michael Turquette <mturquette@baylibre.com>,
	Jiri Slaby <jirislaby@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Charles Keepax <ckeepax@opensource.wolfsonmicro.com>,
	Ryu Euiyoul <ryu.real@samsung.com>,
	Tom Gall <tom.gall@linaro.org>,
	Sumit Semwal <sumit.semwal@linaro.org>,
	John Stultz <john.stultz@linaro.org>,
	Amit Pundir <amit.pundir@linaro.org>,
	devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-clk@vger.kernel.org, linux-gpio@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-samsung-soc@vger.kernel.org,
	linux-serial@vger.kernel.org
Subject: Re: [PATCH v2 4/8] tty: serial: samsung: Init USI to keep clocks running
Date: Mon, 9 Aug 2021 12:45:50 +0200	[thread overview]
Message-ID: <85df3188-0227-f926-61bf-30db1a5ef41d@canonical.com> (raw)
In-Reply-To: <20210806152146.16107-5-semen.protsenko@linaro.org>

On 06/08/2021 17:21, Sam Protsenko wrote:
> 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.
> 
> Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
> ---
> Changes in v2:
>   - Non-intrusive modification of USI registers
>   - Improved comments
>   - Rearranged USI register definitions to conform with existing style
> 
>  drivers/tty/serial/samsung_tty.c | 32 +++++++++++++++++++++++++++++++-
>  include/linux/serial_s3c.h       |  9 +++++++++
>  2 files changed, 40 insertions(+), 1 deletion(-)
> 


Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>



Best regards,
Krzysztof

  reply	other threads:[~2021-08-09 10:46 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-06 15:21 [PATCH v2 0/8] Add minimal support for Exynos850 SoC Sam Protsenko
2021-08-06 15:21 ` [PATCH v2 1/8] dt-bindings: pinctrl: samsung: Add Exynos850 doc Sam Protsenko
2021-08-06 15:21 ` [PATCH v2 2/8] pinctrl: samsung: Add Exynos850 SoC specific data Sam Protsenko
2021-08-09 10:43   ` Krzysztof Kozlowski
2021-08-09 18:18     ` Sam Protsenko
2021-08-06 15:21 ` [PATCH v2 3/8] dt-bindings: serial: samsung: Add Exynos850 doc Sam Protsenko
2021-08-06 15:21 ` [PATCH v2 4/8] tty: serial: samsung: Init USI to keep clocks running Sam Protsenko
2021-08-09 10:45   ` Krzysztof Kozlowski [this message]
2021-08-06 15:21 ` [PATCH v2 5/8] tty: serial: samsung: Fix driver data macros style Sam Protsenko
2021-08-06 15:21 ` [PATCH v2 6/8] tty: serial: samsung: Add Exynos850 SoC data Sam Protsenko
2021-08-09 10:46   ` Krzysztof Kozlowski
2021-08-06 15:21 ` [PATCH v2 7/8] clk: samsung: Add Exynos850 clock driver stub Sam Protsenko
2021-08-09 10:55   ` Krzysztof Kozlowski
2021-08-09 18:51     ` Sam Protsenko
2021-08-09 11:22   ` Krzysztof Kozlowski
2021-08-09 19:48     ` Sam Protsenko
2021-08-10  7:55       ` Sylwester Nawrocki
2021-08-11 11:20         ` Sam Protsenko
2021-08-06 15:21 ` [PATCH v2 8/8] arm64: dts: exynos: Add Exynos850 SoC support Sam Protsenko

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