Date:   Mon, 15 Oct 2018 10:04:13 +0800
From:   Honghui Zhang <honghui.zhang@...iatek.com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>
CC:     <bhelgaas@...gle.com>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>, <linux-pci@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <ryder.lee@...iatek.com>,
        <ulf.hansson@...aro.org>, <marc.zyngier@....com>,
        <matthias.bgg@...il.com>, <devicetree@...r.kernel.org>,
        <yingjoe.chen@...iatek.com>, <eddie.huang@...iatek.com>,
        <youlin.pei@...iatek.com>, <yt.shen@...iatek.com>,
        <sean.wang@...iatek.com>
Subject: Re: [PATCH v6 2/9] PCI: mediatek: Fixup class ID for MT7622 as
 PCI_CLASS_BRIDGE_PCI

On Fri, 2018-10-12 at 11:22 +0100, Lorenzo Pieralisi wrote:
> On Fri, Oct 12, 2018 at 04:01:29PM +0800, Honghui Zhang wrote:
> > On Thu, 2018-10-11 at 12:38 +0100, Lorenzo Pieralisi wrote:
> > > On Tue, Oct 09, 2018 at 11:08:15AM +0800, Honghui Zhang wrote:
> > > > On Mon, 2018-10-08 at 18:23 +0100, Lorenzo Pieralisi wrote:
> > > > > On Mon, Oct 08, 2018 at 11:24:41AM +0800, honghui.zhang@...iatek.com wrote:
> > > > > > From: Honghui Zhang <honghui.zhang@...iatek.com>
> > > > > > 
> > > > > > The PCIe controller of MT7622 has TYPE 1 configuration space type, but
> > > > > > the HW default class type values is invalid.
> > > > > > 
> > > > > > The commit 101c92dc80c8 ("PCI: mediatek: Set up vendor ID and class
> > > > > > type for MT7622") have set the class ID for MT7622 as
> > > > > > PCI_CLASS_BRIDGE_HOSTe, but it's not workable for MT7622:
> > > > > > 
> > > > > > In __pci_bus_assign_resources, the framework only setup bridge's
> > > > > > resource window only if class type is PCI_CLASS_BRIDGE_PCI. Or it
> > > > > > will leave the subordinary PCIe device's MMIO window un-touched.
> > > 
> > > Can you please provide me with a full log of the issue ?
> > > 
> > > What is the bug this patch is actually fixing ?
> > > 
> > > > > > Fixup the class type to PCI_CLASS_BRIDGE_PCI as most of the controller
> > > > > > driver do.
> > > > > 
> > > > > I think that this patch is correct but the commit log fails to pin point
> > > > > the problem. The IP you are programming is a root port, that's why you
> > > > > have to have the proper class code, the patch looks fine but I would
> > > > > like to peek Bjorn's brain on this since it is a fundamental concept.
> > > > > 
> > > > 
> > > > I'm a bit confused with the concepts of PCI_CLASS_BRIDGE_HOST and
> > > > PCI_CLASS_BRIDGE_PCI, from PCI express spec,
> > > > 4.0r1.0(PCI_Express_Base_4.0r1.0_September-27-2017-c), Host Bridge is
> > > > "part of a Root Complex that connects a host CPU or CPUs to a
> > > > Hierarchy". While Root Complex defines as "A defined System Element that
> > > > includes at least one Host Bridge, Root port, or Root complex Integrated
> > > > Endpoint".
> > > > 
> > > > But according to my understanding, most of the root port IPs integrated
> > > > with a "PCI_CLASS_BRIDGE_PCI", which has type 1 configuration space and
> > > > could be saw as a pci device when using lspci.
> > > > 
> > > > And for MT7622, it integrated with block of internal control registers,
> > > > type 1 configuration space, and is considered as a root complex.
> > > 
> > > I assume you mean a type 1 config header here. I do not think it
> > > is mandatory for a host bridge to have a type 1 config header
> > > (and related bridge windows + primary/secondary/subordinate bus
> > > numbers) but I do not know how the IP you are programming is
> > > designed.
> > 
> > Yes, MT7622 has the type 1 config header and related bridge windows and
> > primary/secondary/subordinate bus numbers.
> > 
> > > 
> > > If the host bridge needs its memory window to be configured you can
> > > easily do that in the driver (with driver specific code) without
> > > requiring the generic PCI resource core to do that for you, the host
> > > bridge is the root of the bus I do not see any reason why it should
> > > be up to core PCI code to assign it, it is preprogrammed.
> > > 
> > Thanks for explain this.
> > Yes, the MT7622 bridge needs its memory window to be configured but I
> > prefer the PCI resource core to do this for the following reasons:
> > 1. MTK have MT7622 and MT2712, they pretty much using the same IP, but
> > have different memory window base. Currently we using device tree to
> > pass the memory window base. Take using of PCI resource core code to
> > parse and assign those resource will release the burden of driver.
> > 2. I do not want to re-implement the resource parse code to get the
> > memory base from device node. And hard code the memory base in driver is
> > not quite elegant.
> > 3. Most of the host driver which I referenced are using the PCI resource
> > core to help with it's memory window configure, I guess following the
> > majority way maybe better even they may have slit different of the IP
> > design from MTK.
> > 4. Passing the memory base in device node make it more flexible to
> > change the memory window base (in the HW acceptable range) in case of
> > some special EP device required some special PCI address range.
> > 5. MT7622 and MT2712 have the pretty much same IP only MT7622's HW has
> > set the class type to an un-proper class type. Set it to the same values
> > as MT2712 is an easy way to fix.
> 
> We do what needs to be done. From what you are saying, your IP
> implements a config 1 type header and that defines it as a PCI-to-PCI
> bridge (eg a root port, of sorts).
> 
> The points you are making above are software, I understand them but
> that's not what we are discussing here.
> 
> I want you to define the class of your IP according to what your IP
> is and it seems _reasonable_ to me to define the IP as a PCI-to-PCI
> bridge class from the information you are providing.
> 
> I would like you to:
> 
> 1) Rewrite the commit log and explain why your IP needs class
>    reprogramming. I do not care about driver software complexity,
>    I want you to describe how HW works. I do not want you to define
>    a class for your IP because that makes the driver simpler, I want
>    you to define a class for your IP to describe to the kernel what
>    that IP really is, which is different things.
> 2) Define and report the bug you are fixing in the commit log
> 3) Provide a Fixes: tag pointing at the faulty commit

Thanks for your explain, I will follow your suggest in the next version.

Thanks.

> Thanks for your time providing information.
> 
> Lorenzo
> 
> > thanks.
> > > > I'm not sure which CLASS type it should have:
> > > > From PCI_Code-ID_r_1_10__v8-Nov_2017, class type of
> > > > 0x0604(PCI_CLASS_BRIDGE_PCI) is defined as a PCI-to-PCI bridge, not
> > > > literally suitable for MT7622(which is a root complex)(In my personal
> > > > opinion). But it is the only workable CLASS type for MT7622 in current
> > > > kernel.
> > > > 
> > > > > If the kernel does not assign resources unless it detects a
> > > > > PCI_CLASS_BRIDGE_PCI this means that for components that are
> > > > > actually PCI_CLASS_BRIDGE_HOST their register set must come
> > > > > preprogrammed unless I am missing something.
> > > > > 
> > > > 
> > > > In the function pci_request_resource_alignment, it will by pass the
> > > > resource assignment for PCI_CLASS_BRIDGE_HOST, though I'm not figured
> > > > out why.
> > > > 
> > > > > I would like to get to the bottom of this since it is a fundamental
> > > > > enumeration concept.
> > > > > 
> > > > 
> > > > Do you like me to re-write the commit message for this patch and put the
> > > > above information in? Or just not mention the PCI_CLASS_BRIDGE_HOST
> > > > assign resource routine?
> > > 
> > > I want to understand where the problem is and whether it is right to
> > > define the component as a PCI bridge rather than a host bridge.
> > > 
> > 
> > I will update the commit message (put some of the above reasons in the
> > commit message) and send a new version of this patch if it's acceptable
> > for you.
> > 
> > Thanks
> > > Lorenzo
> > 
> > 
> > 

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