RE: [PATCH 04/13] soc: samsung: Add Exynos USI driver

["Chanho Park" <chanho61.park@samsung.com>]

> -----Original Message-----
> From: U-Boot <u-boot-bounces@lists.denx.de> On Behalf Of Sam Protsenko
> Sent: Wednesday, December 13, 2023 12:17 PM
> To: Minkyu Kang <mk7.kang@samsung.com>; Tom Rini <trini@konsulko.com>;
> Lukasz Majewski <lukma@denx.de>; Sean Anderson <seanga2@gmail.com>
> Cc: Simon Glass <sjg@chromium.org>; Heinrich Schuchardt
> <xypron.glpk@gmx.de>; u-boot@lists.denx.de
> Subject: [PATCH 04/13] soc: samsung: Add Exynos USI driver
> 
> USIv2 IP-core is found on modern ARM64 Exynos SoCs (like Exynos850) and
> provides selectable serial protocol (one of: UART, SPI, I2C). USIv2
> registers usually reside in the same register map as a particular
> underlying protocol it implements, but have some particular offset. E.g.
> on Exynos850 the USI_UART has 0x13820000 base address, where UART
> registers have 0x00..0x40 offsets, and USI registers have 0xc0..0xdc
> offsets. Desired protocol can be chosen via SW_CONF register from System
> Register block of the same domain as USI.
> 
> Before starting to use a particular protocol, USIv2 must be configured
> properly:
>   1. Select protocol to be used via System Register
>   2. Clear "reset" flag in USI_CON
>   3. Configure HWACG behavior (e.g. for UART Rx the HWACG must be
>      disabled, so that the IP clock is not gated automatically); this is
>      done using USI_OPTION register
>   4. Keep both USI clocks (PCLK and IPCLK) running during USI registers
>      modification
> 
> This driver implements the above behavior. Of course, USIv2 driver
> should be probed before UART/I2C/SPI drivers. It can be achieved by
> embedding UART/I2C/SPI nodes inside of the USI node (in Device Tree);
> driver then walks underlying nodes and instantiates those. Driver also
> handles USI configuration on PM resume, as register contents can be lost
> during CPU suspend.
> 
> This driver is designed with different USI versions in mind. So it
> should be relatively easy to add new USI revisions to it later.
> 
> Driver's code was copied over from Linux kernel [1] and adapted
> correspondingly for U-Boot API. UCLASS_MISC is used, and although no
> misc operations are implemented, it makes it easier to probe the driver
> this way (as compared to UCLASS_NOP) and keep the code compact.
> 
> [1] drivers/soc/samsung/exynos-usi.c
> 
> Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>

Reviewed-by: Chanho Park <chanho61.park@samsung.com>