linux-kernel - Re: [PATCH v16 6/6] soc: amd: Add support for AMD Pensando SoC Controller

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Message-ID: <CAHp75VdV+2q2_W9buoL-SCO-NkNo2AU1KuiWkFBPDHOhV7b4wA@mail.gmail.com>
Date:   Mon, 25 Sep 2023 11:51:47 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Brad Larson <blarson@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        "linux-mmc @ vger . kernel . org" <linux-mmc@...r.kernel.org>,
        linux-spi@...r.kernel.org, Adrian Hunter <adrian.hunter@...el.com>,
        alcooperx@...il.com, brendan.higgins@...ux.dev,
        Brian Norris <briannorris@...omium.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Conor Dooley <conor+dt@...nel.org>,
        David Gow <davidgow@...gle.com>, gsomlo@...il.com,
        Greg Ungerer <gerg@...ux-m68k.org>,
        Hal Feng <hal.feng@...rfivetech.com>,
        Hitomi Hasegawa <hasegawa-hitomi@...itsu.com>,
        Jonathan Neuschäfer <j.neuschaefer@....net>,
        Joel Stanley <joel@....id.au>,
        Emil Renner Berthing <kernel@...il.dk>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        krzysztof.kozlowski+dt@...aro.org, Lee Jones <lee@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Randy Dunlap <rdunlap@...radead.org>,
        Rob Herring <robh+dt@...nel.org>,
        Samuel Holland <samuel@...lland.org>,
        Serge Semin <fancer.lancer@...il.com>,
        Shuah Khan <skhan@...uxfoundation.org>,
        suravee.suthikulpanit@....com,
        Tom Lendacky <thomas.lendacky@....com>,
        Tony Huang <tonyhuang.sunplus@...il.com>,
        Ulf Hansson <ulf.hansson@...aro.org>, vaishnav.a@...com,
        Walker Chen <walker.chen@...rfivetech.com>,
        Will Deacon <will@...nel.org>,
        Yinbo Zhu <zhuyinbo@...ngson.cn>, devicetree@...r.kernel.org
Subject: Re: [PATCH v16 6/6] soc: amd: Add support for AMD Pensando SoC Controller

On Fri, Sep 22, 2023 at 1:24 PM Arnd Bergmann <arnd@...db.de> wrote:
> On Wed, Sep 13, 2023, at 17:49, Brad Larson wrote:

...

> > v15 changes:
> > - Drop custom ioctl and use existing miscdevice interface.
> > - Delete unused definitions in amd-pensando-ctrl.h
> > - Makefile change to compile for ARCH_PENSANDO
>
> Hi Brad,
>
> I'm sorry I've been out of the loop for so long, and I hope
> we can find a way to manage your SoC support soon. My impression
> is that the normal support patches (1, 3, 4, and 5) are largely
> uncontroversial, while the SoC controller support seems like
> we are still not converging onto something that is ready to
> merge, so I would suggest you split the two parts and send
> the basic support for inclusion in linux-6.7 while we continue
> to discuss the soc controller driver.
>
> Please remove any references to the soc controller from the
> dts files and send that first series to:soc@...nel.org
> cc:linux-arm-kernel (and the other interested parties) so
> I can pick those up.
>
> Regarding the soc controller driver, let me try to give
> you my impression of where we are:
>
> - you have gone through 16 revisions already, which is way
>   too much for a public review, we should have been able
>   to find a solution earlier than that, and this is partly
>   our fault on the reviewer side, and I'm sorry about that.
>
> - Andy's latest comments and a lot of the earlier reviews
>   were focused on implementation details. While those comments
>   are helpful suggestions for improving the code, they miss
>   the larger point about the system design that I'm worried
>   about and probably don't help you actually get it merged.

True. The fact that the new versions left the design remaining make me
think that the ABI was settled down.

> - The main problem I still see is that this driver completely
>   bypasses our normal kernel abstractions and instead creates
>   a low-level passthrough interface for handling kernel
>   functionality in userspace. This creates a liability both
>   for the user ABI and the kernel implementation and prevents
>   any
>
> - There is a chance that your design is in fact the
>   best way to handle this particular hardware, but it is
>   your job to write a convincing explanation of why this
>   platform is different from all the others in the patch
>   description. Your current one-paragraph text does not
>   explain this at all.
>
> I would suggest you prioritize getting the other patches
> included for the moment, but we can keep discussion the
> API design for this driver either in this thread or on the
> #armlinux IRC channel (irc.libera.chat) in parallel if you
> like. In order to help you here, I would need either
> the documentation of the SPI software interface, or the
> source code for the userspace tool.



-- 
With Best Regards,
Andy Shevchenko