[PATCH] pci: Handle 5-bit and 8-bit tag field

[Pierre Moreau <dev-WLoDKDh+7sdAfugRpC6u6w@public.gmane.org>]

If the hardware supports extended tag field (8-bit ones), then enabled it. This
is usually done by the VBIOS, but not on some MBPs (see fdo#86537).
In case extended tag field is not supported, 5-bit tag field is used which
limits the possible values to 32. Apparently bits 7:0 of 0x8841c stores some
number of outstanding requests, so cap it to 32 if extended tag is unsupported.

Fixes: fdo#86537
Signed-off-by: Pierre Moreau <dev@pmoreau.org>
---
 drm/nouveau/nvkm/subdev/pci/base.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/drm/nouveau/nvkm/subdev/pci/base.c b/drm/nouveau/nvkm/subdev/pci/base.c
index d1c148e..70631b3 100644
--- a/drm/nouveau/nvkm/subdev/pci/base.c
+++ b/drm/nouveau/nvkm/subdev/pci/base.c
@@ -46,6 +46,14 @@ nvkm_pci_wr32(struct nvkm_pci *pci, u16 addr, u32 data)
 	pci->func->wr32(pci, addr, data);
 }
 
+u32
+nvkm_pci_mask(struct nvkm_pci *pci, u16 addr, u32 mask, u32 add)
+{
+	u32 data = pci->func->rd32(pci, addr);
+	pci->func->wr32(pci, addr, (data & ~mask) | add);
+	return data;
+}
+
 void
 nvkm_pci_rom_shadow(struct nvkm_pci *pci, bool shadow)
 {
@@ -115,6 +123,23 @@ nvkm_pci_init(struct nvkm_subdev *subdev)
 	if (ret)
 		return ret;
 
+	if (pci_is_pcie(pdev)) {
+		/* Tag field is 8-bit long, regardless of EXT_TAG.
+		 * However, if EXT_TAG is disabled, only the lower 5 bits of the tag
+		 * field should be used, limiting the number of request to 32.
+		 *
+		 * Apparently, 0x041c stores some limit on the number of requests
+		 * possible, so if EXT_TAG is disabled, limit that requests number to
+		 * 32
+		 *
+		 * Fixes fdo#86537
+		 */
+		if (nvkm_pci_rd32(pci, 0x007c) & 0x00000020)
+			nvkm_pci_mask(pci, 0x0080, 0x00000000, 0x00000100);
+		else
+			nvkm_pci_mask(pci, 0x041c, 0x00000060, 0x00000000);
+	}
+
 	pci->irq = pdev->irq;
 	return ret;
 }
-- 
2.5.1

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