linux-kernel - Re: [PATCH] soc: hisilicon: Support HCCS driver on Kunpeng SoC

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Date:   Tue, 16 May 2023 15:35:30 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     "lihuisong (C)" <lihuisong@...wei.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Bjorn Andersson <andersson@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Shawn Guo <shawnguo@...nel.org>, linux-kernel@...r.kernel.org,
        soc@...nel.org, wanghuiqiang@...wei.com, tanxiaofei@...wei.com,
        liuyonglong@...wei.com, huangdaode@...wei.com,
        Sudeep Holla <sudeep.holla@....com>,
        linux-acpi@...r.kernel.org, Len Brown <lenb@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        devicetree@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Subject: Re: [PATCH] soc: hisilicon: Support HCCS driver on Kunpeng SoC

On Tue, May 16, 2023 at 10:13:58PM +0800, lihuisong (C) wrote:
[...]

>
> But I still need the device-flags to report if use PCC operation Region.
> If so I have to dig one address register from comm subspace, right?

[...]

> Thanks for you bringing it up.
> Indeed, this HCCS_DEV_FLAGS_INTR_B is not good.
> I'm going to replace it with PCC operation Region flag.

>From the above 2, I am getting a sense that all these flags dance is for
sharing a PCC subspace ID between this driver and the firmware PCC Opregion ?
If so that may not work as the current implementation of PCC Opregion
assumes the exclusive access to the channel. Since it is initialised
quite early, Opregion must succeed to get the mbox channel acquired and
this driver must fail if they are sharing the channel. Making the sharing
across firmware and this driver may need changes in the PCC Opregion
support code. One possible way is to acquire and release the channel for
each transaction which will be definitely overhead.

-- 
Regards,
Sudeep