Hi Pingfan,
You're welcome. I guess you are referring to the following code,
static void pci_device_shutdown(struct device *dev)
{
struct pci_dev *pci_dev = to_pci_dev(dev);
struct pci_driver *drv = pci_dev->driver;
pm_runtime_resume(dev);
if (drv && drv->shutdown)
drv->shutdown(pci_dev);
/*
* If this is a kexec reboot, turn off Bus Master bit on the
* device to tell it to not continue to do DMA. Don't touch
* devices in D3cold or unknown states.
* If it is not a kexec reboot, firmware will hit the PCI
* devices with big hammer and stop their DMA any way.
*/
if (kexec_in_progress && (pci_dev->current_state <= PCI_D3hot))
pci_clear_master(pci_dev);
}
but it just disables the i915 device as a DMA master, not prevent DMA access
to i915 device.
Thanks,
Jia
-----Original Message-----
From: Pingfan Liu <[email protected]>
Sent: Tuesday, October 7, 2025 10:18 PM
To: Yao, Jia <[email protected]>
Cc: [email protected]; Zuo, Alex <[email protected]>; Lin,
Shuicheng <[email protected]>; Askar Safin <[email protected]>; Chris
Wilson <[email protected]>
Subject: Re: [PATCH v2] drm/i915: Setting/clearing the memory access bit when
en/disabling i915
Hi Jia,
Thanks for the patch, please see the comments below.
On Wed, Oct 8, 2025 at 4:25 AM Jia Yao <[email protected]> wrote:
>
> Make i915's PCI device management more robust by always
> setting/clearing the memory access bit when enabling/disabling the
> device, and by consolidating this logic into helper functions.
>
> It fixes kexec reboot issue by disabling memory access before shutting
> down the device, which can block unsafe and unwanted access from DMA.
>
PCI_COMMAND_MEMORY blocks the access to i915 PCI_COMMAND_MASTER blocks i915
from accessing the system memory.
In the case of kexec-reboot, I think PCI_COMMAND_MASTER has been set on all pci
devices. So I can not figure out how clearing PCI_COMMAND_MEMORY can help in
this case.
Can you explain a little bit?
Thanks,
Pingfan
> v2:
> - follow brace style
>
> Link: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/14598
> Cc: Alex Zuo <[email protected]>
> Cc: Shuicheng Lin <[email protected]>
> Cc: Askar Safin <[email protected]>
> Cc: Pingfan Liu <[email protected]>
> Suggested-by: Chris Wilson <[email protected]>
> Signed-off-by: Jia Yao <[email protected]>
> ---
> drivers/gpu/drm/i915/i915_driver.c | 35
> +++++++++++++++++++++++++++---
> 1 file changed, 32 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_driver.c
> b/drivers/gpu/drm/i915/i915_driver.c
> index b46cb54ef5dc..766f85726b67 100644
> --- a/drivers/gpu/drm/i915/i915_driver.c
> +++ b/drivers/gpu/drm/i915/i915_driver.c
> @@ -118,6 +118,33 @@
>
> static const struct drm_driver i915_drm_driver;
>
> +static int i915_enable_device(struct pci_dev *pdev) {
> + u32 cmd;
> + int ret;
> +
> + ret = pci_enable_device(pdev);
> + if (ret)
> + return ret;
> +
> + pci_read_config_dword(pdev, PCI_COMMAND, &cmd);
> + if (!(cmd & PCI_COMMAND_MEMORY))
> + pci_write_config_dword(pdev, PCI_COMMAND, cmd |
> + PCI_COMMAND_MEMORY);
> +
> + return 0;
> +}
> +
> +static void i915_disable_device(struct pci_dev *pdev) {
> + u32 cmd;
> +
> + pci_read_config_dword(pdev, PCI_COMMAND, &cmd);
> + if (cmd & PCI_COMMAND_MEMORY)
> + pci_write_config_dword(pdev, PCI_COMMAND, cmd &
> + ~PCI_COMMAND_MEMORY);
> +
> + pci_disable_device(pdev);
> +}
> +
> static int i915_workqueues_init(struct drm_i915_private *dev_priv) {
> /*
> @@ -788,7 +815,7 @@ int i915_driver_probe(struct pci_dev *pdev, const struct
> pci_device_id *ent)
> struct intel_display *display;
> int ret;
>
> - ret = pci_enable_device(pdev);
> + ret = i915_enable_device(pdev);
> if (ret) {
> pr_err("Failed to enable graphics device: %pe\n",
> ERR_PTR(ret));
> return ret;
> @@ -796,7 +823,7 @@ int i915_driver_probe(struct pci_dev *pdev, const
> struct pci_device_id *ent)
>
> i915 = i915_driver_create(pdev, ent);
> if (IS_ERR(i915)) {
> - pci_disable_device(pdev);
> + i915_disable_device(pdev);
> return PTR_ERR(i915);
> }
>
> @@ -885,7 +912,7 @@ int i915_driver_probe(struct pci_dev *pdev, const struct
> pci_device_id *ent)
> enable_rpm_wakeref_asserts(&i915->runtime_pm);
> i915_driver_late_release(i915);
> out_pci_disable:
> - pci_disable_device(pdev);
> + i915_disable_device(pdev);
> i915_probe_error(i915, "Device initialization failed (%d)\n", ret);
> return ret;
> }
> @@ -1003,6 +1030,7 @@ void i915_driver_shutdown(struct
> drm_i915_private *i915)
>
> intel_dmc_suspend(display);
>
> + intel_pxp_fini(i915);
> i915_gem_suspend(i915);
>
> /*
> @@ -1020,6 +1048,7 @@ void i915_driver_shutdown(struct drm_i915_private *i915)
> enable_rpm_wakeref_asserts(&i915->runtime_pm);
>
> intel_runtime_pm_driver_last_release(&i915->runtime_pm);
> + i915_disable_device(to_pci_dev(i915->drm.dev));
> }
>
> static bool suspend_to_idle(struct drm_i915_private *dev_priv)
> --
> 2.34.1
>
