linux-kernel - Re: [PATCH 0/2] Introduce PCI_FIXUP

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Date:   Wed, 27 May 2020 21:51:13 +0800
From:   Zhangfei Gao <zhangfei.gao@...aro.org>
To:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Joerg Roedel <joro@...tes.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Hanjun Guo <guohanjun@...wei.com>,
        Sudeep Holla <sudeep.holla@....com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        jean-philippe <jean-philippe@...aro.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        kenneth-lee-2012@...mail.com, Wangzhou <wangzhou1@...ilicon.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>,
        "open list:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-pci <linux-pci@...r.kernel.org>
Subject: Re: [PATCH 0/2] Introduce PCI_FIXUP_IOMMU



On 2020/5/27 下午5:53, Arnd Bergmann wrote:
> On Wed, May 27, 2020 at 11:00 AM Greg Kroah-Hartman
> <gregkh@...uxfoundation.org> wrote:
>> On Tue, May 26, 2020 at 07:49:07PM +0800, Zhangfei Gao wrote:
>>> Some platform devices appear as PCI but are actually on the AMBA bus,
>> Why would these devices not just show up on the AMBA bus and use all of
>> that logic instead of being a PCI device and having to go through odd
>> fixes like this?
> There is a general move to having hardware be discoverable even with
> ARM processors. Having on-chip devices be discoverable using PCI config
> space is how x86 SoCs usually do it, and that is generally a good thing
> as it means we don't need to describe them in DT
>
> I guess as the hardware designers are still learning about it, this is not
> always done correctly. In general, we can also describe PCI devices on
> DT and do fixups during the probing there, but I suspect that won't work
> as easily using ACPI probing, so the fixup is keyed off the hardware ID,
> again as is common for x86 on-chip devices.
>
>   
Yes, thanks Arnd :)

In order to use pasid, io page fault has to be supported,
either by PCI PRI feature (from pci device) or stall mode from smmu 
(platform device).
Here is letting system know the platform device can support smmu stall 
mode, as a result support pasid.
While stall is not a pci capability, so we use a fixup here.

Thanks