linux-kernel - Re: [PATCH v3 0/5] soc: samsung: Add USI driver

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Message-ID: <fb31a159-6d2e-6c9a-439f-f19ef4fd4732@canonical.com>
Date:   Sun, 5 Dec 2021 17:24:18 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
To:     Sam Protsenko <semen.protsenko@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jaewon Kim <jaewon02.kim@...sung.com>,
        Chanho Park <chanho61.park@...sung.com>,
        David Virag <virag.david003@...il.com>,
        Youngmin Nam <youngmin.nam@...sung.com>,
        devicetree@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-samsung-soc@...r.kernel.org
Subject: Re: [PATCH v3 0/5] soc: samsung: Add USI driver

On 04/12/2021 20:57, Sam Protsenko wrote:
> USIv2 IP-core provides selectable serial protocol (UART, SPI or
> High-Speed I2C); only one can be chosen at a time. This series
> implements USIv2 driver, which allows one to select particular USI
> function in device tree, and also performs USI block initialization.
> 
> With that driver implemented, it's not needed to do USI initialization
> in protocol drivers anymore, so that code is removed from the serial
> driver.
> 
> Because USI driver is tristate (can be built as a module), serial driver
> was reworked so it's possible to use its console part as a module too.
> This way we can load serial driver module from user space and still have
> serial console functional.
> 
> Design features:
>   - "reg" property contains USI registers start address (0xc0 offset);
>     it's used in the driver to access USI_CON and USI_OPTION registers.
>     This way all USI initialization (reset, HWACG, etc) can be done in
>     USIv2 driver separately, rather than duplicating that code over
>     UART/SPI/I2C drivers
>   - System Register (system controller node) and its SW_CONF register
>     offset are provided in "samsung,sysreg" property; it's used to
>     select USI function (protocol to be used)
>   - USI function is specified in "samsung,mode" property; integer value
>     is used to simplify parsing
>   - there is "samsung,clkreq-on" bool property, which makes driver
>     disable HWACG control (needed for UART to work properly)
>   - PCLK and IPCLK clocks are both provided to USI node; apparently both
>     need to be enabled to access USI registers
>   - protocol nodes are embedded (as a child nodes) in USI node; it
>     allows correct init order, and reflects HW properly
>   - USI driver is a tristate: can be also useful from Android GKI
>     requirements point of view
>   - driver functions are implemented with further development in mind:
>     - we might want to add some DebugFs interface later
>     - some functions might need to be revealed to serial drivers with
>       EXPORT_SYMBOL(), and provide somehow pointer to needed USI driver
>       instance
>     - another USI revisions could be added (like USIv1)
> 
> Changes in v3:
>   - Renamed compatible from samsung,exynos-usi-v2 to samsung,exynos850-usi
>   - Used clk_bulk API instead of handling each clock separately
>   - Spell check fixes and coding style fixes
>   - Improved dt-bindings doc
> 
> Changes in v2:
>   - Renamed all 'usi_v2' wording to just 'usi' everywhere
>   - Removed patches adding dependency on EXYNOS_USI for UART/I2C/SPI
>     drivers
>   - Added patch: "tty: serial: samsung: Fix console registration from
>     module"
>   - Combined dt-bindings doc and dt-bindings header patches
>   - Reworked USI driver to be ready for USIv1 addition
>   - Improved dt-bindings
>   - Added USI_V2_NONE mode value
> 
> Sam Protsenko (5):
>   dt-bindings: soc: samsung: Add Exynos USI bindings
>   soc: samsung: Add USI driver
>   tty: serial: samsung: Remove USI initialization
>   tty: serial: samsung: Enable console as module
>   tty: serial: samsung: Fix console registration from module
> 

All this looks good to me. The serial driver changes should come
together with this one (usi driver is now a dependency for them). If I
am correct, mention this please in future cover letter (if there is such).

I will still need DTSI changes for Exynos Auto v9 and confirmation that
is not being used downstream and breaking DTB ABI is okay. Because this
will be a non-bisctable and also a DTB ABI break.

Best regards,
Krzysztof