Hi, > -----Original Message----- > From: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxxxxx> > Sent: Tuesday, December 7, 2021 3:24 AM > To: Arnd Bergmann <arnd@xxxxxxxx>; Olof Johansson <olof@xxxxxxxxx> > Cc: Jaewon Kim <jaewon02.kim@xxxxxxxxxxx>; Chanho Park > <chanho61.park@xxxxxxxxxxx>; David Virag <virag.david003@xxxxxxxxx>; > Youngmin Nam <youngmin.nam@xxxxxxxxxxx>; Sam Protsenko > <semen.protsenko@xxxxxxxxxx>; devicetree@xxxxxxxxxxxxxxx; linux- > serial@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; Greg Kroah- > Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; linux- > samsung-soc@xxxxxxxxxxxxxxx; Rob Herring <robh+dt@xxxxxxxxxx> > Subject: Re: [PATCH v3 0/5] soc: samsung: Add USI driver > > On 05/12/2021 17:24, Krzysztof Kozlowski wrote: > > 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. > > +CC Arnd and Olof, > > Dear Arnd and Olof, > > The patchset discussed here reworks recently added USI code to Samsung > Exynos UART driver in a non-bisectable and ABI-breaking way. The existing > code in serial driver was added in v5.15-rc1, however first user - Exyons > Auto v9 - appeared in v5.16-rc1. > > The bisectability and ABI break will affect only newly upstreamed Samsung > Exynos SoC, so for now only Exynos Auto v9. > > The early code has some drawbacks and limitations which came up now when > we want to extend the USI code to support more blocks (I2C, SPI) and > devices (including older Exynos chipsets). Therefore I am planning to make > an ABI break of this features because: > 1. The code was added recently (v5.15-rc1) and users even later (v5.16- > rc1). > 2. Even though code was merged, I consider it still development phase. > Kernel development goes very fast and we do not defer patches waiting for > perfect solution. > 3. There are no known out-of-tree users of this because this is fairly new. > For this I am waiting for confirmation from Chanho (and/or other Samsung > folks). I don't expect there are out of tree users because any mobile or > automotive product will take Samsung vendor sources and recent kernels are > not a base for Samsung vendor kernels. This will be not an issue in my case. Please apply below patch with this series. https://lore.kernel.org/linux-samsung-soc/20211208003946.139423-1-chanho61.park@xxxxxxxxxxx/T/#u Best Regards, Chanho Park
