Re: [Intel-gfx] [PATCH i-g-t 1/2] drm/i915: Add support for LMEM PCIe resizable bar

[Jani Nikula <jani.nikula@linux.intel.com>]

On Thu, 16 Jun 2022, priyanka.dandamudi@intel.com wrote:
> From: Akeem G Abodunrin <akeem.g.abodunrin@intel.com>
>
> This patch adds support for the local memory PICe resizable bar, so that
> local memory can be resized to the maximum size supported by the device,
> and mapped correctly to the PCIe memory bar. It is usual that GPU
> devices expose only 256MB BARs primarily to be compatible with 32-bit
> systems. So, those devices cannot claim larger memory BAR windows size due
> to the system BIOS limitation. With this change, it would be possible to
> reprogram the windows of the bridge directly above the requesting device
> on the same BAR type.
>
> Signed-off-by: Akeem G Abodunrin <akeem.g.abodunrin@intel.com>
> Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
> Cc: Stuart Summers <stuart.summers@intel.com>
> Cc: Michael J Ruhl <michael.j.ruhl@intel.com>
> Cc: Prathap Kumar Valsan <prathap.kumar.valsan@intel.com>
> Signed-off-by: Priyanka Dandamudi <priyanka.dandamudi@intel.com>
> Reviewed-by: Matthew Auld <matthew.auld@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_driver.c | 92 ++++++++++++++++++++++++++++++
>  1 file changed, 92 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/i915_driver.c b/drivers/gpu/drm/i915/i915_driver.c
> index d26dcca7e654..4bdb471cb2e2 100644
> --- a/drivers/gpu/drm/i915/i915_driver.c
> +++ b/drivers/gpu/drm/i915/i915_driver.c
> @@ -303,6 +303,95 @@ static void sanitize_gpu(struct drm_i915_private *i915)
>  		__intel_gt_reset(to_gt(i915), ALL_ENGINES);
>  }
>  
> +static void __release_bars(struct pci_dev *pdev)

What's with the double underscores? 

> +{
> +	int resno;
> +
> +	for (resno = PCI_STD_RESOURCES; resno < PCI_STD_RESOURCE_END; resno++) {
> +		if (pci_resource_len(pdev, resno))
> +			pci_release_resource(pdev, resno);
> +	}
> +}
> +
> +static void
> +__resize_bar(struct drm_i915_private *i915, int resno, resource_size_t size)
> +{
> +	struct pci_dev *pdev = to_pci_dev(i915->drm.dev);
> +	int bar_size = pci_rebar_bytes_to_size(size);
> +	int ret;
> +
> +	__release_bars(pdev);
> +
> +	ret = pci_resize_resource(pdev, resno, bar_size);
> +	if (ret) {
> +		drm_info(&i915->drm, "Failed to resize BAR%d to %dM (%pe)\n",
> +			 resno, 1 << bar_size, ERR_PTR(ret));
> +		return;
> +	}
> +
> +	drm_info(&i915->drm, "BAR%d resized to %dM\n", resno, 1 << bar_size);
> +}
> +
> +/* BAR size starts from 1MB - 2^20 */
> +#define BAR_SIZE_SHIFT 20
> +static resource_size_t
> +__lmem_rebar_size(struct drm_i915_private *i915, int resno)
> +{
> +	struct pci_dev *pdev = to_pci_dev(i915->drm.dev);
> +	u32 rebar = pci_rebar_get_possible_sizes(pdev, resno);
> +	resource_size_t size;
> +
> +	if (!rebar)
> +		return 0;
> +
> +	size = 1ULL << (__fls(rebar) + BAR_SIZE_SHIFT);
> +
> +	if (size <= pci_resource_len(pdev, resno))
> +		return 0;
> +
> +	return size;
> +}
> +
> +#define LMEM_BAR_NUM 2
> +static void i915_resize_lmem_bar(struct drm_i915_private *i915)
> +{
> +	struct pci_dev *pdev = to_pci_dev(i915->drm.dev);
> +	struct pci_bus *root = pdev->bus;
> +	struct resource *root_res;
> +	resource_size_t rebar_size = __lmem_rebar_size(i915, LMEM_BAR_NUM);
> +	u32 pci_cmd;
> +	int i;
> +
> +	if (!rebar_size)
> +		return;
> +
> +	/* Find out if root bus contains 64bit memory addressing */
> +	while (root->parent)
> +		root = root->parent;
> +
> +	pci_bus_for_each_resource(root, root_res, i) {
> +		if (root_res && root_res->flags & (IORESOURCE_MEM |
> +					IORESOURCE_MEM_64) && root_res->start > 0x100000000ull)
> +			break;
> +	}
> +
> +	/* pci_resize_resource will fail anyways */
> +	if (!root_res) {
> +		drm_info(&i915->drm, "Can't resize LMEM BAR - platform support is missing\n");
> +		return;
> +	}
> +
> +	/* First disable PCI memory decoding references */
> +	pci_read_config_dword(pdev, PCI_COMMAND, &pci_cmd);
> +	pci_write_config_dword(pdev, PCI_COMMAND,
> +			       pci_cmd & ~PCI_COMMAND_MEMORY);
> +
> +	__resize_bar(i915, LMEM_BAR_NUM, rebar_size);
> +
> +	pci_assign_unassigned_bus_resources(pdev->bus);
> +	pci_write_config_dword(pdev, PCI_COMMAND, pci_cmd);
> +}

Doesn't feel like the above code belongs in this file. The file is
supposed to be very high level. The mchbar stuff is the only low level
thing here, and that feels out of place too. Maybe this and the mchbar
stuff belong in a new file.

BR,
Jani.


> +
>  /**
>   * i915_driver_early_probe - setup state not requiring device access
>   * @dev_priv: device private
> @@ -852,6 +941,9 @@ int i915_driver_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
>  
>  	disable_rpm_wakeref_asserts(&i915->runtime_pm);
>  
> +	if (HAS_LMEM(i915))
> +		i915_resize_lmem_bar(i915);
> +
>  	intel_vgpu_detect(i915);
>  
>  	ret = intel_gt_probe_all(i915);

-- 
Jani Nikula, Intel Open Source Graphics Center