linux-kernel - Re: [PATCH 2/5] dt-bindings: soc: hpe: hpe,gxp-srom.yaml

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Message-ID: <Y8jzsmC3azFgbZLP@enigma.ccjz.io>
Date:   Thu, 19 Jan 2023 15:39:30 +0800
From:   Clay Chang <clayc@....com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        <linux-kernel@...r.kernel.org>, <soc@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <devicetree@...r.kernel.org>,
        "Verdun, Jean-Marie" <verdun@....com>,
        "Hawkins, Nick" <nick.hawkins@....com>,
        Rob Herring <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>,
        Russell King <linux@...linux.org.uk>,
        Olof Johansson <olof@...om.net>
Subject: Re: [PATCH 2/5] dt-bindings: soc: hpe: hpe,gxp-srom.yaml

On Mon, Jan 16, 2023 at 04:18:59PM +0100, Arnd Bergmann wrote:
> On Mon, Jan 16, 2023, at 14:42, Clay Chang wrote:
> > On Thu, Jan 12, 2023 at 02:37:53PM +0100, Arnd Bergmann wrote:
> >> On Thu, Jan 12, 2023, at 14:16, Clay Chang wrote:
> >> For the user interface side, I don't really like the idea of
> >> having a hardware register directly exposed as driver in
> >> drivers/soc, this generally makes it impossible to have portable
> >> userspace that works across implementations of multiple SoC
> >> vendors, and it makes it too easy to come up with an ad-hoc
> >> interface to make a chip work for a particular use case when
> >> a more general solution would be better.
> >> 
> >
> > I agree with you. I have one question though: if we create a 'hpe'
> > directory under drivers/soc, and put all HPE BMC specific drivers there,
> > do you think this proper?
> 
> It certainly wouldn't be right to put "all HPE BMC specific drivers"
> in there. Most drivers will fit into some existing subsystem, and
> should be moved there instead. drivers/soc is used primarily for
> drivers using soc_device_register() to provide information about the
> soc, and we also use it as a place for drivers that just export
> soc-specific helper functions that can be used by other drivers.
> 

Sorry for not saying it clearly. I meant to put those HPE BMC related
drivers that are "not specific" to a particular subsystem in
drivers/soc/hpe. For those fit into some existing subsystems go to their
designated places.

> >> Again, it's hard for me to tell why this even needs to be runtime
> >> configurable, please try to describe what type of application
> >> would access the sysfs interface here, and why this can't just
> >> be set to a fixed value by bootloader or kernel without user
> >> interaction.
> >
> > The register is used for communication and synchronization between the
> > BMC and the host. During runtime, user-space daemons configures the
> > value of the register for interactions.
> 
> That does not sound very specific. What is the subsystem on the
> host that this communicates with? Can you put the driver into the
> same subsystem?
> 
>     Arnd

This is a control register in the BMC chip that partially controls host
boot behaviors. When writing to the register, privileged mode is
required. That's why we rely on a kernel driver for writing to the
control register. And, there is no corresponding subsystem in the host
OS. For this case, is it acceptable to put this driver under
drivers/soc/hpe?

Thanks,
Clay