linux-kernel - Re: [PATCH v5 01/14] drivers: iommu: add FWNODE

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Message-ID: <20160930090702.GA7725@red-moon>
Date:   Fri, 30 Sep 2016 10:07:02 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     iommu@...ts.linux-foundation.org, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will.deacon@....com>,
        Marc Zyngier <marc.zyngier@....com>,
        Robin Murphy <robin.murphy@....com>,
        Tomasz Nowicki <tn@...ihalf.com>,
        Hanjun Guo <hanjun.guo@...aro.org>,
        Jon Masters <jcm@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Sinan Kaya <okaya@...eaurora.org>,
        Nate Watterson <nwatters@...eaurora.org>,
        Prem Mallappa <prem.mallappa@...adcom.com>,
        Dennis Chen <dennis.chen@....com>, linux-acpi@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v5 01/14] drivers: iommu: add FWNODE_IOMMU fwnode type

On Thu, Sep 29, 2016 at 10:59:40PM +0200, Rafael J. Wysocki wrote:
> On Thursday, September 29, 2016 03:15:20 PM Lorenzo Pieralisi wrote:
> > Hi Rafael,
> > 
> > On Fri, Sep 09, 2016 at 03:23:30PM +0100, Lorenzo Pieralisi wrote:
> > > On systems booting with a device tree, every struct device is
> > > associated with a struct device_node, that represents its DT
> > > representation. The device node can be used in generic kernel
> > > contexts (eg IRQ translation, IOMMU streamid mapping), to
> > > retrieve the properties associated with the device and carry
> > > out kernel operation accordingly. Owing to the 1:1 relationship
> > > between the device and its device_node, the device_node can also
> > > be used as a look-up token for the device (eg looking up a device
> > > through its device_node), to retrieve the device in kernel paths
> > > where the device_node is available.
> > > 
> > > On systems booting with ACPI, the same abstraction provided by
> > > the device_node is required to provide look-up functionality.
> > > 
> > > Therefore, mirroring the approach implemented in the IRQ domain
> > > kernel layer, this patch adds an additional fwnode type FWNODE_IOMMU.
> > > 
> > > This patch also implements a glue kernel layer that allows to
> > > allocate/free FWNODE_IOMMU fwnode_handle structures and associate
> > > them with IOMMU devices.
> > > 
> > > Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
> > > Reviewed-by: Hanjun Guo <hanjun.guo@...aro.org>
> > > Cc: Joerg Roedel <joro@...tes.org>
> > > Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> > > ---
> > >  include/linux/fwnode.h |  1 +
> > >  include/linux/iommu.h  | 25 +++++++++++++++++++++++++
> > >  2 files changed, 26 insertions(+)
> > > 
> > > diff --git a/include/linux/fwnode.h b/include/linux/fwnode.h
> > > index 8516717..6e10050 100644
> > > --- a/include/linux/fwnode.h
> > > +++ b/include/linux/fwnode.h
> > > @@ -19,6 +19,7 @@ enum fwnode_type {
> > >  	FWNODE_ACPI_DATA,
> > >  	FWNODE_PDATA,
> > >  	FWNODE_IRQCHIP,
> > > +	FWNODE_IOMMU,
> > 
> > This patch provides groundwork for this series and it is key for
> > the rest of it, basically the point here is that we need a fwnode
> > to differentiate platform devices created out of static ACPI tables
> > entries (ie IORT), that represent IOMMU components.
> > 
> > The corresponding device is not an ACPI device (I could fabricate one as
> > it is done for other static tables entries eg FADT power button, but I
> > do not necessarily see the reason for doing that given that all we need
> > the fwnode for is a token identifier), so FWNODE_ACPI does not apply
> > here.
> > 
> > Please let me know if it is reasonable how I sorted this out (it
> > is basically identical to IRQCHIP, just another enum entry), the
> > remainder of the code depends on this.
> 
> I'm not familiar with the use case, so I don't see anything unreasonable
> in it.

The use case is pretty simple: on ARM SMMU devices are platform devices.
When booting with DT they are identified through an of_node and related
FWNODE_OF type. When booting with ACPI, the ARM SMMU platform devices,
to be equivalent to DT booting path, should be created out of static
IORT table entries (that's how we describe SMMUs); we need to create
a fwnode "token" to associate with those platform devices and that's
not a FWNODE_ACPI (that is for an ACPI device firmware object, here we
really do not need one), so this patch.

> If you're asking about whether or not I mind adding more fwnode types in
> principle, then no, I don't. :-) 

Yes, that's what I was asking, the only point that bugs me is that for
both FWNODE_IRQCHIP and FWNODE_IOMMU the fwnode is just a "token" (ie a
valid pointer) used for look-up and the type in the fwnode_handle is
mostly there for error checking, I was wondering if we could create a
specific fwnode_type for this specific usage (eg FWNODE_TAG and then add
a type to it as part of its container struct) instead of adding an enum
value per subsystem - it seems there are other fwnode types in the
pipeline :), so I am asking:

lkml.kernel.org/r/3D1468514043-21081-3-git-send-email-minyard@....org

If it is ok for you and Joerg I will go ahead with current patch
keeping in mind that the above should not be that complicated to
implement if we deem it reasonable.

Thanks,
Lorenzo