drm/radeon/kms: make sure pci max read request size is valid on evergreen+ (v2)

If the bios or OS sets the pci max read request size to 0 or an
invalid value (6,7), it can result in a hang or slowdown. Check
and set it to something sane if it's invalid.

Fixes:
https://bugzilla.kernel.org/show_bug.cgi?id=42162

v2: use pci reg defines from include/linux/pci_regs.h

Signed-off-by: Alex Deucher <[e-mail]>
Cc: [e-mail]
Reviewed-by: Michel Dänzer <[e-mail]>
Signed-off-by: Dave Airlie <[e-mail]>

drivers/gpu/drm/radeon/evergreen.c

···
 void evergreen_fini(struct radeon_device *rdev);
 static void evergreen_pcie_gen2_enable(struct radeon_device *rdev);
 
+void evergreen_fix_pci_max_read_req_size(struct radeon_device *rdev)
+{
+	u16 ctl, v;
+	int cap, err;
+
+	cap = pci_pcie_cap(rdev->pdev);
+	if (!cap)
+		return;
+
+	err = pci_read_config_word(rdev->pdev, cap + PCI_EXP_DEVCTL, &ctl);
+	if (err)
+		return;
+
+	v = (ctl & PCI_EXP_DEVCTL_READRQ) >> 12;
+
+	/* if bios or OS sets MAX_READ_REQUEST_SIZE to an invalid value, fix it
+	 * to avoid hangs or perfomance issues
+	 */
+	if ((v == 0) || (v == 6) || (v == 7)) {
+		ctl &= ~PCI_EXP_DEVCTL_READRQ;
+		ctl |= (2 << 12);
+		pci_write_config_word(rdev->pdev, cap + PCI_EXP_DEVCTL, ctl);
+	}
+}
+
 void evergreen_pre_page_flip(struct radeon_device *rdev, int crtc)
 {
 	/* enable the pflip int */
···
 	}
 
 	WREG32(GRBM_CNTL, GRBM_READ_TIMEOUT(0xff));
+
+	evergreen_fix_pci_max_read_req_size(rdev);
 
 	cc_gc_shader_pipe_config = RREG32(CC_GC_SHADER_PIPE_CONFIG) & ~2;
 

drivers/gpu/drm/radeon/ni.c

···
 extern void evergreen_mc_program(struct radeon_device *rdev);
 extern void evergreen_irq_suspend(struct radeon_device *rdev);
 extern int evergreen_mc_init(struct radeon_device *rdev);
+extern void evergreen_fix_pci_max_read_req_size(struct radeon_device *rdev);
 
 #define EVERGREEN_PFP_UCODE_SIZE 1120
 #define EVERGREEN_PM4_UCODE_SIZE 1376
···
 	}
 
 	WREG32(GRBM_CNTL, GRBM_READ_TIMEOUT(0xff));
+
+	evergreen_fix_pci_max_read_req_size(rdev);
 
 	mc_shared_chmap = RREG32(MC_SHARED_CHMAP);
 	mc_arb_ramcfg = RREG32(MC_ARB_RAMCFG);