Re: [PATCH v2 17/17] drm/i915: Properly request PCI BARs

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Oct 09, 2020 at 09:59:34AM +0200, Daniel Vetter wrote:
> When trying to test my CONFIG_IO_STRICT_DEVMEM changes I realized they
> do nothing for i915. Because i915 doesn't request any regions, like
> pretty much all drm pci drivers. I guess this is some very old
> remnants from the userspace modesetting days, when we wanted to
> co-exist with the fbdev driver. Which usually requested these
> resources.
> 
> But makes me wonder why the pci subsystem doesn't just request
> resource automatically when we map a bar and a pci driver is bound?
> 
> Knowledge about which pci bars we need kludged together from
> intel_uncore.c and intel_gtt.c from i915 and intel-gtt.c over in the
> fake agp driver.
> 
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Jason Gunthorpe <jgg@ziepe.ca>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: John Hubbard <jhubbard@nvidia.com>
> Cc: Jérôme Glisse <jglisse@redhat.com>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: linux-mm@kvack.org
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-samsung-soc@vger.kernel.org
> Cc: linux-media@vger.kernel.org
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Cc: linux-pci@vger.kernel.org
> ---
>  drivers/gpu/drm/i915/intel_uncore.c | 25 +++++++++++++++++++++++--
>  1 file changed, 23 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index 54e201fdeba4..ce39049d8919 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -1692,10 +1692,13 @@ static int uncore_mmio_setup(struct intel_uncore *uncore)
>  	struct pci_dev *pdev = i915->drm.pdev;
>  	int mmio_bar;
>  	int mmio_size;
> +	int bar_selection;

Signed bitmasks always make me uneasy. But looks like
that's what it is in the pci api. So meh.

> +	int ret;
>  
>  	mmio_bar = IS_GEN(i915, 2) ? 1 : 0;
> +	bar_selection = BIT (2) | BIT(mmio_bar);
                           ^
spurious space			   

That's also not correct for gen2 I think.

gen2:
0 = GMADR
1 = MMADR
2 = IOBAR

gen3:
0 = MMADR
1 = IOBAR
2 = GMADR
3 = GTTADR

gen4+:
0+1 = GTTMMADR
2+3 = GMADR
4 = IOBAR

Maybe we should just have an explicit list of bars like that in a
comment?

I'd also suggest sucking this bitmask calculation into a small helper
so you can reuse it for the release.

>  	/*
> -	 * Before gen4, the registers and the GTT are behind different BARs.
> +	 * On gen3 the registers and the GTT are behind different BARs.
>  	 * However, from gen4 onwards, the registers and the GTT are shared
>  	 * in the same BAR, so we want to restrict this ioremap from
>  	 * clobbering the GTT which we want ioremap_wc instead. Fortunately,
> @@ -1703,6 +1706,8 @@ static int uncore_mmio_setup(struct intel_uncore *uncore)
>  	 * generations up to Ironlake.
>  	 * For dgfx chips register range is expanded to 4MB.
>  	 */
> +	if (INTEL_GEN(i915) == 3)
> +		bar_selection |= BIT(3);
>  	if (INTEL_GEN(i915) < 5)
>  		mmio_size = 512 * 1024;
>  	else if (IS_DGFX(i915))
> @@ -1710,8 +1715,15 @@ static int uncore_mmio_setup(struct intel_uncore *uncore)
>  	else
>  		mmio_size = 2 * 1024 * 1024;
>  
> +	ret = pci_request_selected_regions(pdev, bar_selection, "i915");
> +	if (ret < 0) {
> +		drm_err(&i915->drm, "failed to request pci bars\n");
> +		return ret;
> +	}
> +
>  	uncore->regs = pci_iomap(pdev, mmio_bar, mmio_size);
>  	if (uncore->regs == NULL) {
> +		pci_release_selected_regions(pdev, bar_selection);
>  		drm_err(&i915->drm, "failed to map registers\n");
>  		return -EIO;
>  	}
> @@ -1721,9 +1733,18 @@ static int uncore_mmio_setup(struct intel_uncore *uncore)
>  
>  static void uncore_mmio_cleanup(struct intel_uncore *uncore)
>  {
> -	struct pci_dev *pdev = uncore->i915->drm.pdev;
> +	struct drm_i915_private *i915 = uncore->i915;
> +	struct pci_dev *pdev = i915->drm.pdev;
> +	int mmio_bar;
> +	int bar_selection;
> +
> +	mmio_bar = IS_GEN(i915, 2) ? 1 : 0;
> +	bar_selection = BIT (2) | BIT(mmio_bar);
> +	if (INTEL_GEN(i915) == 3)
> +		bar_selection |= BIT(3);
>  
>  	pci_iounmap(pdev, uncore->regs);
> +	pci_release_selected_regions(pdev, bar_selection);
>  }
>  
>  void intel_uncore_init_early(struct intel_uncore *uncore,
> -- 
> 2.28.0
> 
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-- 
Ville Syrjälä
Intel