On 18/11/2021 20:59, Sam Protsenko wrote:

On Tue, 16 Nov 2021 at 11:32, Krzysztof Kozlowski
[off-list ref] wrote:

quoted

On 16/11/2021 02:12, Chanho Park wrote:

quoted

quoted

With this patch the Exynos850 HSI2C becomes functional. The only nit-pick
from my side (just a food for thought): do we want to configure USI
related config inside of particular drivers (SPI, I2C, UART)? Or it would
be better design to implement some platform driver for that, so we can
choose USI configuration (SPI/I2C/UART) in device tree? I think this
series is good to be merged as is, but we should probably consider all
upsides and downsides of each option, for the future work.

I'm also considering how to support this USI configuration gracefully.
Current version of USI is v2 which means there is a v1 version as well. It might be a non-upstream SoC so we don't need to consider it so far.
But, there is a possibility that the USI hw version can be bumped for future SoCs.

As you probably know, earlier version of the product kernel has a USI SoC driver[1] and it was designed to be configured the USI settings by device tree.

Option1) Make a USI driver under soc/samsung/ like [1].
Option2) Use more generic driver such as "reset driver"? This might be required to extend the reset core driver.
Option3) Each USI driver(uart/i2c/spi) has its own USI configurations respectively and expose some configurations which can be variable as device tree.

[1]: https://github.com/ianmacd/d2s/blob/master/drivers/soc/samsung/usi_v2.c

I don't have user manuals, so all my knowledge here is based on
Exynos9825 vendor source code, therefore it is quite limited. In
devicetree the USI devices have their own nodes - but does it mean it's
separate SFR range dedicated to USI? Looks like that, especially that
address space is just for one register (4 bytes).

In such case having separate dedicated driver makes sense and you would
only have to care about driver ordering (e.g. via device links or phandles).

Option 2 looks interesting - reusing reset framework to set proper USI
mode, however this looks more like a hack. As you said Chanho, if there
is a USI version 3, this reset framework might not be sufficient.

In option 3 each driver (UART/I2C/SPI) would need to receive second IO
range and toggle some registers, which could be done via shared
function. If USI v3 is coming, all such drivers could get more complicated.

I think option 1 is the cleanest and extendable in future. It's easy to
add usi-v3 or whatever without modifying the UART/I2C/SPI drivers. It
also nicely encapsulates USI-related stuff in separate driver. Probe
ordering should not be a problem now.

But as I said, I don't have even the big picture here, so I rely on your
opinions more.

Hi Krzysztof,

Can you please let me know if you're going to apply this series as is,
or if you want me to submit USIv2 driver first, and then rework this
patch on top of it? I'm working on some HSI2C related patches right
now, and thus it'd nice to know about your decision on this series
beforehand, as some of my patches (like bindings doc patches) might
depend on it. Basically I'd like to base my patches on the proper
baseline, so we don't have to rebase those later.

This set won't go via my tree anyway, but I am against it. David pointed
out that his USIv1 is a little bit different and embedding in each of
I2C/UART/SPI drivers the logic of controlling USIv1 and USIv2 looks too
big. The solution with a dedicated driver looks to me more flexible and
encapsulated/cleaner.

Therefore after the discussions I am against this solution, so a
soft-NAK from my side.


Best regards,
Krzysztof

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