drm/nouveau/pci: Handle 5-bit and 8-bit tag field

If the hardware supports extended tag field (8-bit ones), then enable 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 number of requests to 32. Apparently bits 7:0 of
0x08841c stores some number of outstanding requests, so cap it to 32 if
extended tag is unsupported.

Fixes: fdo#86537

v2: Restrict changes to chipsets >= 0x84
v3:
  * Add nvkm_pci_mask to pci.h
  * Mask bit 8 before setting it
v4:
  * Rename `add` argument of nvkm_pci_mask to `value`
  * Move code from nvkm_pci_init to g84_pci_init and remove PCIe and chipset
    checks
v5:
  * Rebase code on latest PCI structure
  * Restore PCIe check
  * Fix namings in nvkm_pci_mask
  * Rephrase part of the commit message
Signed-off-by: Pierre Moreau <pierre.morrow@free.fr>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/include/nvkm/subdev/pci.h

@@ -24,6 +24,7 @@ struct nvkm_pci {
 u32 nvkm_pci_rd32(struct nvkm_pci *, u16 addr);
 void nvkm_pci_wr08(struct nvkm_pci *, u16 addr, u8 data);
 void nvkm_pci_wr32(struct nvkm_pci *, u16 addr, u32 data);
+u32 nvkm_pci_mask(struct nvkm_pci *, u16 addr, u32 mask, u32 value);
 void nvkm_pci_rom_shadow(struct nvkm_pci *, bool shadow);
 
 int nv04_pci_new(struct nvkm_device *, int, struct nvkm_pci **);

drivers/gpu/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 value)
+{
+	u32 data = pci->func->rd32(pci, addr);
+	pci->func->wr32(pci, addr, (data & ~mask) | value);
+	return data;
+}
+
 void
 nvkm_pci_rom_shadow(struct nvkm_pci *pci, bool shadow)
 {

drivers/gpu/drm/nouveau/nvkm/subdev/pci/g84.c

@@ -25,8 +25,32 @@
 
 #include <core/pci.h>
 
+void
+g84_pci_init(struct nvkm_pci *pci)
+{
+	/* The following only concerns PCIe cards. */
+	if (!pci_is_pcie(pci->pdev))
+		return;
+
+	/* 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, 0x00000100, 0x00000100);
+	else
+		nvkm_pci_mask(pci, 0x041c, 0x00000060, 0x00000000);
+}
+
 static const struct nvkm_pci_func
 g84_pci_func = {
+	.init = g84_pci_init,
 	.rd32 = nv40_pci_rd32,
 	.wr08 = nv40_pci_wr08,
 	.wr32 = nv40_pci_wr32,

drivers/gpu/drm/nouveau/nvkm/subdev/pci/g94.c

@@ -25,6 +25,7 @@
 
 static const struct nvkm_pci_func
 g94_pci_func = {
+	.init = g84_pci_init,
 	.rd32 = nv40_pci_rd32,
 	.wr08 = nv40_pci_wr08,
 	.wr32 = nv40_pci_wr32,

drivers/gpu/drm/nouveau/nvkm/subdev/pci/gf100.c

@@ -31,6 +31,7 @@ gf100_pci_msi_rearm(struct nvkm_pci *pci)
 
 static const struct nvkm_pci_func
 gf100_pci_func = {
+	.init = g84_pci_init,
 	.rd32 = nv40_pci_rd32,
 	.wr08 = nv40_pci_wr08,
 	.wr32 = nv40_pci_wr32,

drivers/gpu/drm/nouveau/nvkm/subdev/pci/priv.h

@@ -20,4 +20,6 @@ void nv40_pci_wr32(struct nvkm_pci *, u16, u32);
 void nv40_pci_msi_rearm(struct nvkm_pci *);
 
 void nv46_pci_msi_rearm(struct nvkm_pci *);
+
+void g84_pci_init(struct nvkm_pci *pci);
 #endif