Re: [Qemu-devel] [Intel-gfx] ResettRe: [Xen-devel] [v5][PATCH 0/5] xen: add Intel IGD passthrough support

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Thu, Jul 24, 2014 at 09:44:41AM +0800, Chen, Tiejun wrote:
> On 2014/7/24 4:54, Konrad Rzeszutek Wilk wrote:
> >On Sat, Jul 19, 2014 at 12:27:21AM +0000, Kay, Allen M wrote:
> >>>For the MCH PCI registers that do need to be read - can you tell us which ones those are?
> >>
> >>In qemu/hw/xen_pt_igd.c/igd_pci_read(), following MCH PCI config register reads are passthrough to the host HW.   Some of the registers are needed by Ironlake GFX driver which we probably can remove.  I did a trace recently on Broadwell,  the number of register accessed are even smaller (0, 2, 2c, 2e, 50, 52, a0, a4).  Given that we now have integrated MCH and GPU in the same socket, looks like driver can easily remove reads for offsets 0 - 0x2e.
> >>
> >>		case 0x00:        /* vendor id */
> >>		case 0x02:        /* device id */
> >>		case 0x08:        /* revision id */
> >>		case 0x2c:        /* sybsystem vendor id */
> >>		case 0x2e:        /* sybsystem id */
> >
> >Right. We can fix the i915 to use the mechanism that Michael mentioned.
> >(see attached RFC patches)
> >
> >>		case 0x50:        /* SNB: processor graphics control register */
> >>		case 0x52:        /* processor graphics control register */
> >>		case 0xa0:        /* top of memory */
> >>		case 0xb0:        /* ILK: BSM: should read from dev 2 offset 0x5c */
> >>		case 0x58:        /* SNB: PAVPC Offset */
> >>		case 0xa4:        /* SNB: graphics base of stolen memory */
> >>		case 0xa8:        /* SNB: base of GTT stolen memory */
> >
> >I dug in the intel-gtt.c (see ironlake_gtt_driver) to figure out this
> >a bit more. As in, I speculated, what if we returned 0 (and not implement
> >any support for reading from these registers). What would happen?
> >
> >0x52 for Ironlake (g5):
> >------------------
> >It looks like intel_gmch_probe is called when i915_gem_gtt_init
> >starts (there is a lot of code that looks to be used between
> >intel-gtt.c and i915.c).
> >
> >Anyhow the interesting parts are that i9xx_setup ends up calling
> >ioremap the i915 BAR to setup some of these registers for older generations.
> >
> >Then i965_gtt_total_entries gets which reads 0x52, but it is only
> >needed for v5 generation. For other (v4 and G33) it reads it from the GPU's
> >0x2020  register.
> >
> >If there is a mismatch, it writes to the GPU at 0x2020 to update the
> >the size based on the bridge. And then it reads from 0x2020 and that
> >is returned and stuck in  intel_private.gtt_total_entries.
> >
> >So 0x52 in the emulated bridge could be populated with what the
> >GPU has at 0x2020. And the writes go in the emulated area.
> >
> >0x52 for v6 -> v8:
> >-----------------
> >We seem to go to gen6_gmch_probe which just figures out the
> >the GTT based on the GPU's BAR sizes. The stolen values
> >are read from 0x50 from the GPU. So no need to touch the bridge
> >(see gen6_gmch_probe)
> >
> >OK, so no need to have 0x52 or 0x50 in the bridge.
> >
> >0xA0:
> >---------
> >Could not find any reference in the Linux code. Why would
> >Windows driver need this? If we returned the _real_ TOM would
> >it matter? Is it used to figure out the device should use 32-bit
> >DMA operations or 40-bit?
> >
> >0xb0 or 0x5c:
> >-------------
> >No mention of them in the Linux code.
> >
> >0x58, 0xa4, 0xa8:
> >-----------------
> >No usage of them in the Linux code. We seem to be using the 0x52
> >from the bridge and 0x2020 from the GPU for this functionality.
> >
> >
> >So in theory*, if using Ironlake we need to have a proper value
> >in 0x52 in the bridge. But for the later chipsets we do not need
> >these values (I am assuming that intel_setup_mchbar can safely
> >return as it does that for Ironlake and could very well for later
> >generations).
> >
> >Can this be reflected in the Windows driver as well?
> >
> >P.S.
> >*theory: That is assuming we modify the Linux i915_drv.c:intel_detect_pch
> >to pick up the id as suggested earlier. See the RFC patches attached.
> >(Not compile tested at all!)
> 
> I take a look these patches, looks we still scan all PCI Bridge to walk all
> PCHs. So this means we still need to fake a PCI bridge, right? Or maybe you
> don't cover this problem this time.

I totally forgot. Feel free to fix that.
> 
> I prefer we should check dev slot to get that PCH like my previous patch,

Uh? Your patch was checking for 0:1f.0, not the slot of the device.

(see https://lkml.org/lkml/2014/6/19/121)
> "gpu:drm:i915:intel_detect_pch: back to check devfn instead of check class
> type". Because Windows always use this way, so I think this point should be
> same between Linux and Windows.

Didn't we discuss that we did not want to pass in PCH at all if we can?

And from the observation I made above it seems that we can safely do it
under Linux. With Windows I don't know - but I presume the answer is yes too.


> 
> Or we need anther better way to unify all OSs.

Yes. The observation is that a lot of these registers are aliased in the GPU.
As such we can skip some of this bridge poking. Hm. I should have gotten
further and also done this on baremetal, but figured as an RFC it would
paint a picture of what we had in mind?

> 
> Thanks
> Tiejun
> 
> >>
> >>Allen
> >>
> >>-----Original Message-----
> >>From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@oracle.com]
> >>Sent: Friday, July 18, 2014 6:45 AM
> >>To: Kay, Allen M
> >>Cc: Michael S. Tsirkin; Jesse Barnes; peter.maydell@linaro.org; xen-devel@lists.xensource.com; Ross Philipson; airlied@linux.ie; daniel.vetter@ffwll.ch; intel-gfx@lists.freedesktop.org; Kelly.Zytaruk@amd.com; qemu-devel@nongnu.org; Anthony Perard; Stefano Stabellini; anthony@codemonkey.ws; Paolo Bonzini; Zhang, Yang Z; Chen, Tiejun
> >>Subject: Re: [Intel-gfx] ResettRe: [Xen-devel] [v5][PATCH 0/5] xen: add Intel IGD passthrough support
> >>
> >>On Thu, Jul 17, 2014 at 05:37:12PM +0000, Kay, Allen M wrote:
> >>>>That sounds great. Tiejun could you confirm that with windows driver guys too?
> >>>
> >>>I believe windows driver can also assume specific CPU/PCH combos.  I will discuss this with native Windows driver guys.  Preferably, the same code path can be used for both native and virtualization cases to avoid frequent breakage as most developers and QA do not test new code changes in virtualization environment.
> >>>
> >>>I have verified that Windows driver do not need to write to any MCH PCI registers on HSW/BDW so the PCI write function can be removed.  The  MCH PCI registers that need to be read, we are working with HW team to get them mirrored in GPU MMIO registers in future HW.
> >>>
> >>
> >>For the MCH PCI registers that do need to be read - can you tell us which ones those are?
> >>
> >>Thank you!
> >>>Allen
> >>>
> >>>-----Original Message-----
> >>>From: Intel-gfx [mailto:intel-gfx-bounces@lists.freedesktop.org] On
> >>>Behalf Of Michael S. Tsirkin
> >>>Sent: Thursday, July 03, 2014 1:28 PM
> >>>To: Jesse Barnes
> >>>Cc: peter.maydell@linaro.org; xen-devel@lists.xensource.com; Ross
> >>>Philipson; Konrad Rzeszutek Wilk; airlied@linux.ie;
> >>>daniel.vetter@ffwll.ch; intel-gfx@lists.freedesktop.org;
> >>>Kelly.Zytaruk@amd.com; qemu-devel@nongnu.org; Anthony Perard; Stefano
> >>>Stabellini; anthony@codemonkey.ws; Paolo Bonzini; Zhang, Yang Z; Chen,
> >>>Tiejun
> >>>Subject: Re: [Intel-gfx] ResettRe: [Xen-devel] [v5][PATCH 0/5] xen:
> >>>add Intel IGD passthrough support
> >>>
> >>>On Thu, Jul 03, 2014 at 12:09:28PM -0700, Jesse Barnes wrote:
> >>>>On Thu, 3 Jul 2014 14:26:12 -0400
> >>>>Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> wrote:
> >>>>
> >>>>>On Thu, Jul 03, 2014 at 10:32:12AM +0300, Michael S. Tsirkin wrote:
> >>>>>>On Wed, Jul 02, 2014 at 12:23:37PM -0400, Konrad Rzeszutek Wilk wrote:
> >>>>>>>On Wed, Jul 02, 2014 at 04:50:15PM +0200, Paolo Bonzini wrote:
> >>>>>>>>Il 02/07/2014 16:00, Konrad Rzeszutek Wilk ha scritto:
> >>>>>>>>>With this long thread I lost a bit context about the
> >>>>>>>>>challenges that exists. But let me try summarizing it here
> >>>>>>>>>- which will hopefully get some consensus.
> >>>>>>>>>
> >>>>>>>>>1). Fix IGD hardware to not use Southbridge magic addresses.
> >>>>>>>>>    We can moan and moan but I doubt it is going to change.
> >>>>>>>>
> >>>>>>>>There are two problems:
> >>>>>>>>
> >>>>>>>>- Northbridge (i.e. MCH i.e. PCI host bridge) configuration
> >>>>>>>>space addresses
> >>>>>>>
> >>>>>>>Right. So in  drivers/gpu/drm/i915/i915_dma.c:
> >>>>>>>1135 #define MCHBAR_I915 0x44
> >>>>>>>1136 #define MCHBAR_I965 0x48
> >>>>>>>
> >>>>>>>1147         int reg = INTEL_INFO(dev)->gen >= 4 ? MCHBAR_I965 : MCHBAR_I915;
> >>>>>>>1152         if (INTEL_INFO(dev)->gen >= 4)
> >>>>>>>1153                 pci_read_config_dword(dev_priv->bridge_dev, reg + 4, &temp_hi);
> >>>>>>>1154         pci_read_config_dword(dev_priv->bridge_dev, reg, &temp_lo);
> >>>>>>>1155         mchbar_addr = ((u64)temp_hi << 32) | temp_lo;
> >>>>>>>
> >>>>>>>and
> >>>>>>>
> >>>>>>>1139 #define DEVEN_REG 0x54
> >>>>>>>
> >>>>>>>1193         int mchbar_reg = INTEL_INFO(dev)->gen >= 4 ? MCHBAR_I965 : MCHBAR_I915;
> >>>>>>>1202         if (IS_I915G(dev) || IS_I915GM(dev)) {
> >>>>>>>1203                 pci_read_config_dword(dev_priv->bridge_dev, DEVEN_REG, &temp);
> >>>>>>>1204                 enabled = !!(temp & DEVEN_MCHBAR_EN);
> >>>>>>>1205         } else {
> >>>>>>>1206                 pci_read_config_dword(dev_priv->bridge_dev, mchbar_reg, &temp);
> >>>>>>>1207                 enabled = temp & 1;
> >>>>>>>1208         }
> >>>>>>>>
> >>>>>>>>- Southbridge (i.e. PCH i.e. ISA bridge) vendor/device ID;
> >>>>>>>>some versions of the driver identify it by class, some versions identify it by slot (1f.0).
> >>>>>>>
> >>>>>>>Right, So in  drivers/gpu/drm/i915/i915_drv.c the giant
> >>>>>>>intel_detect_pch which sets the pch_type based on :
> >>>>>>>
> >>>>>>>  432                 if (pch->vendor == PCI_VENDOR_ID_INTEL) {
> >>>>>>>  433                         unsigned short id = pch->device & INTEL_PCH_DEVICE_ID_MASK;
> >>>>>>>  434                         dev_priv->pch_id = id;
> >>>>>>>  435
> >>>>>>>  436                         if (id == INTEL_PCH_IBX_DEVICE_ID_TYPE) {
> >>>>>>>
> >>>>>>>It checks for 0x3b00, 0x1c00, 0x1e00, 0x8c00 and 0x9c00.
> >>>>>>>The INTEL_PCH_DEVICE_ID_MASK is 0xff00
> >>>>>>>>
> >>>>>>>>To solve the first, make a new machine type, PIIX4-based,
> >>>>>>>>and pass through the registers you need.  The patch must
> >>>>>>>>document _exactly_ why the registers are safe to pass.  If
> >>>>>>>>they are not reserved on PIIX4, the patch must document what
> >>>>>>>>the same offsets mean on PIIX4, and why it's sensible to
> >>>>>>>>assume that firmware for virtual machine will not read/write them.  Bonus point for also documenting the same for Q35.
> >>>>>>>
> >>>>>>>OK. They look to be related to setting up an MBAR , but I
> >>>>>>>don't understand why it is needed. Hopefully some of the i915 folks CC-ed here can answer.
> >>>>>>
> >>>>>>In particular, I think setting up MBAR should move out of i915
> >>>>>>and become the bridge driver tweak on linux and windows.
> >>>>>
> >>>>>That is an excellent idea.
> >>>>>
> >>>>>However I am still curious to _why_ it has to be done in the first place.
> >>>>
> >>>>The display part of the GPU is partly on the PCH, and it's possible
> >>>>to mix & match them a bit, so we have this detection code to figure
> >>>>things out.  In some cases, the PCH display portion may not even be
> >>>>present, so we look for that too.
> >>>>
> >>>>Practically speaking, we could probably assume specific CPU/PCH
> >>>>combos, as I don't think they're generally mixed across generations,
> >>>>though SNB and IVB did have compatible sockets, so there is the
> >>>>possibility of mixing CPT and PPT PCHs, but those are register
> >>>>identical as far as the graphics driver is concerned, so even that should be safe.
> >>>>
> >>>>Beyond that, the other MCH data we need to look at is mirrored into
> >>>>the GPU's MMIO space on current gens.  On older gens, we do need to
> >>>>poke at the memory controller a bit to get some info (see
> >>>>intel_setup_mchbar()), but that's not true of newer stuff.  Looks
> >>>>like we only short circuit that on VLV though; we could probably do
> >>>>it on
> >>>>SNB+.
> >>>
> >>>That sounds great. Tiejun could you confirm that with windows driver guys too?
> >>>
> >>>>--
> >>>>Jesse Barnes, Intel Open Source Technology Center
> >>>_______________________________________________
> >>>Intel-gfx mailing list
> >>>Intel-gfx@lists.freedesktop.org
> >>>http://lists.freedesktop.org/mailman/listinfo/intel-gfx