From: Matt Roper <matthew.d.roper@intel.com>
To: Arun R Murthy <arun.r.murthy@intel.com>
Cc: <intel-xe@lists.freedesktop.org>, <Michal.Wajdeczko@intel.com>
Subject: Re: [PATCHv2] drm/xe: Check for dead config space on reading all 1s
Date: Tue, 19 May 2026 13:26:29 -0700 [thread overview]
Message-ID: <20260519202629.GI3397116@mdroper-desk1.amr.corp.intel.com> (raw)
In-Reply-To: <20260519033104.480503-1-arun.r.murthy@intel.com>
On Tue, May 19, 2026 at 09:01:04AM +0530, Arun R Murthy wrote:
> After ioremap the BAR mapped address is read once as a sanity check and
> if found to be all 1s then return avoiding the driver initialization of
> a dead device.
>
> v2: Move the sanity check to mmio_probe_early() - Michal
>
> Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/work_items/7941
> Signed-off-by: Arun R Murthy <arun.r.murthy@intel.com>
> ---
> drivers/gpu/drm/xe/xe_mmio.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>
> diff --git a/drivers/gpu/drm/xe/xe_mmio.c b/drivers/gpu/drm/xe/xe_mmio.c
> index 78adb303b663..d206e3720eed 100644
> --- a/drivers/gpu/drm/xe/xe_mmio.c
> +++ b/drivers/gpu/drm/xe/xe_mmio.c
> @@ -90,6 +90,7 @@ int xe_mmio_probe_early(struct xe_device *xe)
> {
> struct xe_tile *root_tile = xe_device_get_root_tile(xe);
> struct pci_dev *pdev = to_pci_dev(xe->drm.dev);
> + u32 sanity = 0;
>
> /*
> * Map the entire BAR.
> @@ -103,6 +104,21 @@ int xe_mmio_probe_early(struct xe_device *xe)
> return -EIO;
> }
>
> + /*
> + * If the parent PCIe bridge failed to leave D3cold, or the device
> + * fell off the bus, MMIO reads return all-ones. Detect that here
> + * before any other subsystem (SR-IOV, GuC, pcode...) consumes a
> + * bogus 0xFFFFFFFF.
> + */
> + sanity = readl(xe->mmio.regs);
> + if (sanity == U32_MAX && !pci_device_is_present(pdev)) {
Was the && here intended or was that supposed to be an ||? I think if
the device isn't "present" the read would _always_ be a failure and get
terminated with ~0? For that matter, is this the right place to be
checking this? I guess there can be surprise device removal at
absolultely any time, but the most common time this would come back as
false would be if the device got removed during a system suspend; the
code you're adding here only runs on probe and not on resume flows. I
think it would be pretty rare to see pci_device_is_present() already
return false here in the probe path if we just got a successful return
from pci_enable_device()?
I don't think any platform has a register at offset 0, so if the device
is up properly, the bogus read should come back as 0 (and we can
recognize device errors via ~0 reads), but it still might be best to
read a known-extant register offset just to guarantee there's no
undocumented behavior. Maybe GMD_ID would be a good candidate since it
should be non-zero (and non ~0) on all POR platforms, zero (and tested
as such) on the non-POR Xe1 platforms, and is a register that we need to
read early in device init anyway (so we could stash the value and save
ourselves the read later).
Matt
> + drm_err(&xe->drm,
> + "MMIO reads all 1s and device not present; aborting probe\n");
> + pci_iounmap(pdev, xe->mmio.regs);
> + xe->mmio.regs = NULL;
> + return -ENODEV;
> + }
> +
> /* Setup first tile; other tiles (if present) will be setup later. */
> xe_mmio_init(&root_tile->mmio, root_tile, xe->mmio.regs, SZ_4M);
>
> --
> 2.25.1
>
--
Matt Roper
Graphics Software Engineer
Linux GPU Platform Enablement
Intel Corporation
next prev parent reply other threads:[~2026-05-19 20:26 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-12 6:01 [PATCH] drm/xe: Check for dead config space on reading all 1s Arun R Murthy
2026-05-12 11:12 ` ✓ CI.KUnit: success for " Patchwork
2026-05-12 11:55 ` [PATCH] " Michal Wajdeczko
2026-05-12 12:32 ` ✓ Xe.CI.BAT: success for " Patchwork
2026-05-12 22:28 ` ✗ Xe.CI.FULL: failure " Patchwork
2026-05-19 3:31 ` [PATCHv2] " Arun R Murthy
2026-05-19 13:24 ` Raag Jadav
2026-05-20 3:52 ` Murthy, Arun R
2026-05-19 20:26 ` Matt Roper [this message]
2026-05-20 4:42 ` Murthy, Arun R
2026-05-20 18:07 ` Matt Roper
2026-05-21 4:05 ` Murthy, Arun R
2026-07-06 4:41 ` [PATCHv3] drm/xe: Check for dead config space Arun R Murthy
2026-05-19 3:39 ` ✓ CI.KUnit: success for drm/xe: Check for dead config space on reading all 1s (rev2) Patchwork
2026-05-19 4:21 ` ✓ Xe.CI.BAT: " Patchwork
2026-05-19 13:10 ` ✗ Xe.CI.FULL: failure " Patchwork
2026-07-06 4:49 ` ✓ CI.KUnit: success for drm/xe: Check for dead config space on reading all 1s (rev3) Patchwork
2026-07-06 5:31 ` ✗ Xe.CI.BAT: failure " Patchwork
2026-07-06 7:19 ` ✓ Xe.CI.FULL: success " Patchwork
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