linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: "Gupta, Nipun" <Nipun.Gupta@amd.com>
To: Robin Murphy <robin.murphy@arm.com>,
	Saravana Kannan <saravanak@google.com>,
	Jason Gunthorpe <jgg@nvidia.com>
Cc: Greg KH <gregkh@linuxfoundation.org>,
	"robh+dt@kernel.org" <robh+dt@kernel.org>,
	"krzysztof.kozlowski+dt@linaro.org" 
	<krzysztof.kozlowski+dt@linaro.org>,
	"rafael@kernel.org" <rafael@kernel.org>,
	"eric.auger@redhat.com" <eric.auger@redhat.com>,
	"alex.williamson@redhat.com" <alex.williamson@redhat.com>,
	"cohuck@redhat.com" <cohuck@redhat.com>,
	"Gupta, Puneet (DCG-ENG)" <puneet.gupta@amd.com>,
	"song.bao.hua@hisilicon.com" <song.bao.hua@hisilicon.com>,
	"mchehab+huawei@kernel.org" <mchehab+huawei@kernel.org>,
	"maz@kernel.org" <maz@kernel.org>,
	"f.fainelli@gmail.com" <f.fainelli@gmail.com>,
	"jeffrey.l.hugo@gmail.com" <jeffrey.l.hugo@gmail.com>,
	"Michael.Srba@seznam.cz" <Michael.Srba@seznam.cz>,
	"mani@kernel.org" <mani@kernel.org>,
	"yishaih@nvidia.com" <yishaih@nvidia.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"okaya@kernel.org" <okaya@kernel.org>,
	"Anand, Harpreet" <harpreet.anand@amd.com>,
	"Agarwal, Nikhil" <nikhil.agarwal@amd.com>,
	"Simek, Michal" <michal.simek@amd.com>,
	"git (AMD-Xilinx)" <git@amd.com>
Subject: RE: [RFC PATCH v2 2/6] bus/cdx: add the cdx bus driver
Date: Mon, 29 Aug 2022 04:49:02 +0000	[thread overview]
Message-ID: <DM6PR12MB30824C5129A7251C589F1461E8769@DM6PR12MB3082.namprd12.prod.outlook.com> (raw)
In-Reply-To: <a6ca5a5a-8424-c953-6f76-c9212db88485@arm.com>

[AMD Official Use Only - General]



> -----Original Message-----
> From: Robin Murphy <robin.murphy@arm.com>
> Sent: Friday, August 26, 2022 1:28 AM
> To: Saravana Kannan <saravanak@google.com>; Jason Gunthorpe
> <jgg@nvidia.com>
> Cc: Greg KH <gregkh@linuxfoundation.org>; Gupta, Nipun
> <Nipun.Gupta@amd.com>; robh+dt@kernel.org;
> krzysztof.kozlowski+dt@linaro.org; rafael@kernel.org; eric.auger@redhat.com;
> alex.williamson@redhat.com; cohuck@redhat.com; Gupta, Puneet (DCG-ENG)
> <puneet.gupta@amd.com>; song.bao.hua@hisilicon.com;
> mchehab+huawei@kernel.org; maz@kernel.org; f.fainelli@gmail.com;
> jeffrey.l.hugo@gmail.com; Michael.Srba@seznam.cz; mani@kernel.org;
> yishaih@nvidia.com; linux-kernel@vger.kernel.org; devicetree@vger.kernel.org;
> kvm@vger.kernel.org; okaya@kernel.org; Anand, Harpreet
> <harpreet.anand@amd.com>; Agarwal, Nikhil <nikhil.agarwal@amd.com>;
> Simek, Michal <michal.simek@amd.com>; git (AMD-Xilinx) <git@amd.com>
> Subject: Re: [RFC PATCH v2 2/6] bus/cdx: add the cdx bus driver
> 
> [CAUTION: External Email]
> 
> On 2022-08-25 19:38, Saravana Kannan wrote:
> > On Wed, Aug 24, 2022 at 4:31 PM Jason Gunthorpe <jgg@nvidia.com> wrote:
> >>
> >> On Wed, Aug 24, 2022 at 02:11:48PM +0200, Greg KH wrote:
> >>>> We can share the RFC in case you are interested in looking at code flow
> >>>> using the of_dynamic approach.
> >>>
> >>> Please no more abuse of the platform device.
> >>
> >> Last time this came up there was some disagreement from the ARM folks,
> >> they were not keen on having xx_drivers added all over the place to
> >> support the same OF/DT devices just discovered in a different way. It is
> >> why ACPI is mapped to platform_device even in some cases.
> >>
> >> I think if you push them down this path they will get resistance to
> >> get the needed additional xx_drivers into the needed places.
> >>
> >>> If your device can be discovered by scanning a bus, it is not a platform
> >>> device.
> >>
> >> A DT fragment loaded during boot binds a driver using a
> >> platform_driver, why should a DT fragment loaded post-boot bind using
> >> an XX_driver and further why should the CDX way of getting the DT
> >> raise to such importantance that it gets its own cdx_driver ?
> >>
> >> In the end the driver does not care about how the DT was loaded.
> >> None of these things are on a discoverable bus in any sense like PCI
> >> or otherwise. They are devices described by a DT fragement and they
> >> take all their parameters from that chunk of DT.
> >>
> >> How the DT was loaded into the system is not a useful distinction that
> >> raises the level of needing an entire new set of xx_driver structs all
> >> over the tree, IMHO.
> >
> > Jason, I see your point or rather the point the ARM folks might have
> > made. But in this case, why not use DT overlays to add these devices?
> > IIRC there's an in kernel API to add DT overlays. If so, should this
> > be more of a FPGA driver that reads FPGA stuff and adds DT overlays?
> > That'd at least make a stronger case for why this isn't a separate
> > bus.
> 
> Right, that's exactly where this discussion started.
> 
> To my mind, it would definitely help to understand if this is a *real*
> discoverable bus in hardware, i.e. does one have to configure one's
> device with some sort of CDX wrapper at FPGA synthesis time, that then
> physically communicates with some sort of CDX controller to identify
> itself once loaded; or is it "discoverable" in the sense that there's
> some firmware on an MCU controlling what gets loaded into the FPGA, and
> software can query that and get back whatever precompiled DTB fragment
> came bundled with the bitstream, i.e. it's really more like fpga-mgr in
> a fancy hat?

Devices are created in FPFGA with a CDX wrapper, and CDX controller(firmware)
reads that CDX wrapper to find out new devices. Host driver then interacts with
firmware to find newly discovered devices. This bus aligns with PCI infrastructure.
It happens to be an embedded interface as opposed to off-chip connection.

We are trying to do an RFC which proposes CDX as a new bus. It seems to be a
cleaner interface than what was added in RFC v2.

> 
> It's pretty much impossible to judge from all the empty placeholder code
> here how much is real and constrained by hardware and how much is
> firmware abstraction, which makes it particularly hard to review whether
> any proposal heading in the right direction.

You can consider the placeholders for now as API calls which would eventually
communicate with FW, and fetch required info like number of FPGA devices,
device related parameters (vendor_id, device_id etc), and command the
firmware to reset the device.

In next rev, we would add new API stubs instead of empty placeholders (as FW
interaction code is under development), which could give more clear view.

> 
> Even if it *is* entirely firmware smoke-and-mirrors, if that firmware
> can provide a standardised discovery and configuration interface for
> common resources, it can be a bus. But then it should *be* a bus, with
> its own bus_type and its own device type to model those standard
> interfaces and IDs and resources. Or if it is really just a very clever
> dynamic DT overlay manager for platform devices, then it can be that
> instead. But what it should clearly not be is some in-between mess
> making the worst of both worlds, which is what the code here inescapably
> smells of.
> 
> Thanks,
> Robin.

  parent reply	other threads:[~2022-08-29  4:49 UTC|newest]

Thread overview: 113+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-08-03 12:26 [RFC PATCH 0/2] add support for CDX bus MSI domain Nipun Gupta
2022-08-03 12:26 ` [RFC PATCH 1/2] irqchip: cdx-bus: add cdx-MSI domain with gic-its domain as parent Nipun Gupta
2022-08-03 12:33   ` Greg KH
2022-08-03 12:37     ` Gupta, Nipun
2022-08-04  8:49   ` Marc Zyngier
2022-08-04  9:18     ` Gupta, Nipun
     [not found]       ` <87mtckwaxa.wl-maz@kernel.org>
2022-08-04 12:11         ` Gupta, Nipun
2022-08-03 12:26 ` [RFC PATCH 2/2] driver core: add compatible string in sysfs for platform devices Nipun Gupta
2022-08-03 12:31   ` Greg KH
2022-08-03 12:46     ` Gupta, Nipun
2022-08-03 14:16 ` [RFC PATCH 0/2] add support for CDX bus MSI domain Robin Murphy
2022-08-04  4:23   ` Gupta, Nipun
2022-08-17 16:00   ` Jason Gunthorpe
2022-08-17 15:05 ` [RFC PATCH v2 0/6] add support for CDX bus controller Nipun Gupta
2022-08-17 15:05   ` [RFC PATCH v2 1/6] Documentation: DT: Add entry for CDX controller Nipun Gupta
2022-08-18  9:54     ` Krzysztof Kozlowski
2022-08-18  9:59       ` Krzysztof Kozlowski
2022-09-05 14:05       ` Gupta, Nipun
2022-09-06  6:55         ` Krzysztof Kozlowski
2022-09-06  7:03           ` Gupta, Nipun
2022-09-06  7:20             ` Krzysztof Kozlowski
2022-08-17 15:05   ` [RFC PATCH v2 2/6] bus/cdx: add the cdx bus driver Nipun Gupta
2022-08-17 15:32     ` Greg KH
2022-08-17 15:46       ` Marc Zyngier
2022-08-22 13:21       ` Gupta, Nipun
2022-08-22 13:29         ` Greg KH
2022-08-24  8:50           ` Gupta, Nipun
2022-08-24 12:11             ` Greg KH
2022-08-24 23:31               ` Jason Gunthorpe
2022-08-25 18:38                 ` Saravana Kannan
2022-08-25 19:57                   ` Robin Murphy
2022-08-26  0:08                     ` Jason Gunthorpe
2022-08-29  4:49                       ` Gupta, Nipun
2022-08-29  4:49                     ` Gupta, Nipun [this message]
2022-08-29 15:31                       ` Jason Gunthorpe
2022-08-30  7:06                         ` Gupta, Nipun
2022-08-30 11:25                           ` Robin Murphy
2022-08-30 13:01                           ` Jason Gunthorpe
2022-08-30 13:12                             ` Gupta, Nipun
2022-08-17 15:05   ` [RFC PATCH v2 3/6] bus/cdx: add cdx-MSI domain with gic-its domain as parent Nipun Gupta
2022-08-17 15:33     ` Greg KH
2022-08-17 15:05   ` [RFC PATCH v2 4/6] bus/cdx: add rescan and reset support Nipun Gupta
2022-08-17 15:05   ` [RFC PATCH v2 5/6] vfio: platform: reset: add reset for cdx devices Nipun Gupta
2022-08-17 15:05   ` [RFC PATCH v2 6/6] driver core: add compatible string in sysfs for platform devices Nipun Gupta
2022-08-17 15:30     ` Greg KH
2022-08-17 16:04       ` Saravana Kannan
2022-09-05 13:54         ` Gupta, Nipun
2022-09-06 13:47 ` [RFC PATCH v3 0/7] add support for CDX bus Nipun Gupta
2022-09-06 13:47   ` [RFC PATCH v3 1/7] dt-bindings: bus: add CDX bus device tree bindings Nipun Gupta
2022-09-06 17:46     ` Rob Herring
2022-09-07  3:13       ` Gupta, Nipun
2022-09-08 10:51         ` Krzysztof Kozlowski
2022-09-06 13:47   ` [RFC PATCH v3 2/7] bus/cdx: add the cdx bus driver Nipun Gupta
2022-09-07  0:32     ` Saravana Kannan
2022-09-07  3:21       ` Gupta, Nipun
2022-09-07 18:06         ` Saravana Kannan
2022-09-07 12:32     ` Greg KH
2022-09-08 13:29       ` Gupta, Nipun
2022-09-06 13:47   ` [RFC PATCH v3 3/7] iommu/arm-smmu-v3: support ops registration for CDX bus Nipun Gupta
2022-09-07  0:10     ` Saravana Kannan
2022-09-07  3:17       ` Gupta, Nipun
2022-09-07  8:27         ` Robin Murphy
2022-09-07 18:24           ` Saravana Kannan
2022-09-07 20:40             ` Robin Murphy
2022-09-08  0:14               ` Saravana Kannan
2022-09-06 13:47   ` [RFC PATCH v3 4/7] bus/cdx: add cdx-MSI domain with gic-its domain as parent Nipun Gupta
2022-09-06 17:19     ` Jason Gunthorpe
2022-09-07 11:17       ` Marc Zyngier
2022-09-07 11:33         ` Robin Murphy
2022-09-07 12:14           ` Marc Zyngier
2022-09-07 11:35         ` Radovanovic, Aleksandar
     [not found]           ` <87illzuzyw.wl-maz@kernel.org>
2022-09-07 13:18             ` Radovanovic, Aleksandar
     [not found]               ` <87edwmuw4f.wl-maz@kernel.org>
2022-09-08  9:51                 ` Radovanovic, Aleksandar
2022-09-08 11:49                   ` Robin Murphy
2022-09-07 13:18     ` Marc Zyngier
2022-09-08 14:13       ` Gupta, Nipun
     [not found]         ` <87a67aueg7.wl-maz@kernel.org>
2022-09-09  6:32           ` Gupta, Nipun
2022-10-12 10:04       ` Gupta, Nipun
2022-10-12 10:34         ` Radovanovic, Aleksandar
2022-10-12 13:02           ` Jason Gunthorpe
2022-10-12 13:37             ` Radovanovic, Aleksandar
2022-10-12 14:38               ` Jason Gunthorpe
2022-10-12 15:09                 ` Radovanovic, Aleksandar
2022-10-13 12:43                   ` Jason Gunthorpe
2022-10-14 11:18                     ` Radovanovic, Aleksandar
2022-10-14 11:54                       ` gregkh
2022-10-14 12:13                         ` Radovanovic, Aleksandar
2022-10-14 13:46                           ` gregkh
2022-10-14 13:58                       ` Jason Gunthorpe
2022-09-06 13:47   ` [RFC PATCH v3 5/7] bus/cdx: add bus and device attributes Nipun Gupta
2022-09-06 13:48   ` [RFC PATCH v3 6/7] vfio/cdx: add support for CDX bus Nipun Gupta
2022-09-06 17:20     ` Jason Gunthorpe
2022-09-06 17:23       ` Gupta, Nipun
2022-09-06 13:48   ` [RFC PATCH v3 7/7] vfio/cdx: add interrupt support Nipun Gupta
2022-10-14  4:40 ` [RFC PATCH v4 0/8] add support for CDX bus Nipun Gupta
2022-10-14  4:40   ` [RFC PATCH v4 1/8] dt-bindings: bus: add CDX bus device tree bindings Nipun Gupta
2022-10-14 14:17     ` Rob Herring
2022-10-17 10:18       ` Gupta, Nipun
2022-10-14  4:40   ` [RFC PATCH v4 2/8] bus/cdx: add the cdx bus driver Nipun Gupta
2022-10-14  7:15     ` Greg KH
2022-10-14  8:12       ` Gupta, Nipun
2022-10-14  7:18     ` Greg KH
2022-10-14  8:20       ` Gupta, Nipun
2022-10-14  4:40   ` [RFC PATCH v4 3/8] iommu/arm-smmu-v3: support ops registration for CDX bus Nipun Gupta
2022-10-14  4:51     ` Gupta, Nipun
2022-10-14  4:40   ` [RFC PATCH v4 4/8] bux/cdx: support dma configuration for CDX devices Nipun Gupta
2022-10-14  4:40   ` [RFC PATCH v4 5/8] bus/cdx: add bus and device attributes Nipun Gupta
2022-10-14  4:40   ` [RFC PATCH v4 6/8] irq/msi: use implicit msi domain for alloc and free Nipun Gupta
2022-10-14  4:40   ` [RFC PATCH v4 7/8] bus/cdx: add cdx-MSI domain with gic-its domain as parent Nipun Gupta
2022-11-17 19:10     ` Thomas Gleixner
2022-10-14  4:40   ` [RFC PATCH v4 8/8] bus/cdx: add cdx controller Nipun Gupta
2022-10-14 14:10   ` [RFC PATCH v4 0/8] add support for CDX bus Rob Herring
2022-10-17 10:08     ` Gupta, Nipun

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=DM6PR12MB30824C5129A7251C589F1461E8769@DM6PR12MB3082.namprd12.prod.outlook.com \
    --to=nipun.gupta@amd.com \
    --cc=Michael.Srba@seznam.cz \
    --cc=alex.williamson@redhat.com \
    --cc=cohuck@redhat.com \
    --cc=devicetree@vger.kernel.org \
    --cc=eric.auger@redhat.com \
    --cc=f.fainelli@gmail.com \
    --cc=git@amd.com \
    --cc=gregkh@linuxfoundation.org \
    --cc=harpreet.anand@amd.com \
    --cc=jeffrey.l.hugo@gmail.com \
    --cc=jgg@nvidia.com \
    --cc=krzysztof.kozlowski+dt@linaro.org \
    --cc=kvm@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mani@kernel.org \
    --cc=maz@kernel.org \
    --cc=mchehab+huawei@kernel.org \
    --cc=michal.simek@amd.com \
    --cc=nikhil.agarwal@amd.com \
    --cc=okaya@kernel.org \
    --cc=puneet.gupta@amd.com \
    --cc=rafael@kernel.org \
    --cc=robh+dt@kernel.org \
    --cc=robin.murphy@arm.com \
    --cc=saravanak@google.com \
    --cc=song.bao.hua@hisilicon.com \
    --cc=yishaih@nvidia.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).