RE: [PATCH 0/2] Enable MMIO GPIO on BCMBCA

[William Zhang <william.zhang@broadcom.com>]

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Hi Linus,

> -----Original Message-----
> From: Linus Walleij <linus.walleij@linaro.org>
> Sent: Tuesday, September 17, 2024 5:45 AM
> To: Bartosz Golaszewski <brgl@bgdev.pl>; Rob Herring <robh@kernel.org>;
> Krzysztof Kozlowski <krzk+dt@kernel.org>; Conor Dooley
> <conor+dt@kernel.org>; William Zhang <william.zhang@broadcom.com>;
> Florian Fainelli <florian.fainelli@broadcom.com>
> Cc: linux-gpio@vger.kernel.org; devicetree@vger.kernel.org; Linus Walleij
> <linus.walleij@linaro.org>
> Subject: [PATCH 0/2] Enable MMIO GPIO on BCMBCA
>
> The Broadcom BCA (Broadband Access) SoC:s all have a dirt-simple
> MMIO GPIO.
>
> It's exposed as a direction register per 32-bit block at
> (base) and a data register per 32-bit block at (block+0x20).
>
> However I wouldn't want to use any of the old compatibles
> becaus for this undocumented SoC I have a gut feeling that
> there may be registers we don't know about at (block+0x40)
> etc and a separate compatible will be needed to slot in
> a more elaborate driver later.
>
For the BCMBCA SoCs(ARM based Broadcom broadband SoCs),
there is no need to access any register at block+0x40 and beyond
for gpio function to work.   So I think the existing the brcm,bcm6345-gpio
fits the bill very well and don't need a new compatible IMHO.  It is
the same tradition/rule for other blocks like wdt, nand controller
and etc.  We use the oldest chip name that has the common IP.

If we upstream more elaborated driver later,  it will be a dedicated gpio
controller driver and not use this basic mmio gpio and we can have
the new compatible.

> Let's do this the hard way and create a new compatible,
> and probe regular MMIO with that for now.
>
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
> ---
> Linus Walleij (2):
>       dt-bindings: gpio: Add BCMBCA to MMIO compatibles
>       gpio: mmio: Support BCMBCA GPIO compatible
>
>  Documentation/devicetree/bindings/gpio/gpio-mmio.yaml | 1 +
>  drivers/gpio/gpio-mmio.c                              | 1 +
>  2 files changed, 2 insertions(+)
> ---
> base-commit: 98f7e32f20d28ec452afb208f9cffc08448a2652
> change-id: 20240917-bcmbca-gpio-mmio-5da863cf5a5d
>
> Best regards,
> --
> Linus Walleij <linus.walleij@linaro.org>

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