agp/intel-gtt: Add intel_gmch_gtt_read_entry()

JIRA: https://issues.redhat.com/browse/RHEL-113204

commit 8f0d361
Author: Ville Syrjälä <ville.syrjala@linux.intel.com>
Date:   Thu Mar 13 16:08:31 2025 +0200

    agp/intel-gtt: Add intel_gmch_gtt_read_entry()

    i915 wants to read out the PTE(s) populated by the BIOS/GOP
    to verify that the framebuffer is in the correct location.
    Introduce intel_gmch_gtt_read_entry() that reads out the
    PTE and decodes it to a somewhat abstract form. For now
    we just return the dma_addr, present bit, and local memory
    bit. I didn't bother with the snoop bit/etc.

    Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
    Link: https://patchwork.freedesktop.org/patch/msgid/20250313140838.29742-4-ville.syrjala@linux.intel.com
    Reviewed-by: Jouni Högander <jouni.hogander@intel.com>

Signed-off-by: José Expósito <jexposit@redhat.com>

Author: jexposit

drivers/char/agp/intel-gtt.c

@@ -53,6 +53,7 @@ struct intel_gtt_driver {
 	 * of the mmio register file, that's done in the generic code. */
 	void (*cleanup)(void);
 	void (*write_entry)(dma_addr_t addr, unsigned int entry, unsigned int flags);
+	dma_addr_t (*read_entry)(unsigned int entry, bool *is_present, bool *is_local);
 	/* Flags is a more or less chipset specific opaque value.
 	 * For chipsets that need to support old ums (non-gem) code, this
 	 * needs to be identical to the various supported agp memory types! */
@@ -336,6 +337,19 @@ static void i810_write_entry(dma_addr_t addr, unsigned int entry,
 	writel_relaxed(addr | pte_flags, intel_private.gtt + entry);
 }
 
+static dma_addr_t i810_read_entry(unsigned int entry,
+				  bool *is_present, bool *is_local)
+{
+	u32 val;
+
+	val = readl(intel_private.gtt + entry);
+
+	*is_present = val & I810_PTE_VALID;
+	*is_local = val & I810_PTE_LOCAL;
+
+	return val & ~0xfff;
+}
+
 static resource_size_t intel_gtt_stolen_size(void)
 {
 	u16 gmch_ctrl;
@@ -741,6 +755,19 @@ static void i830_write_entry(dma_addr_t addr, unsigned int entry,
 	writel_relaxed(addr | pte_flags, intel_private.gtt + entry);
 }
 
+static dma_addr_t i830_read_entry(unsigned int entry,
+				  bool *is_present, bool *is_local)
+{
+	u32 val;
+
+	val = readl(intel_private.gtt + entry);
+
+	*is_present = val & I810_PTE_VALID;
+	*is_local = false;
+
+	return val & ~0xfff;
+}
+
 bool intel_gmch_enable_gtt(void)
 {
 	u8 __iomem *reg;
@@ -878,6 +905,13 @@ void intel_gmch_gtt_insert_sg_entries(struct sg_table *st,
 }
 EXPORT_SYMBOL(intel_gmch_gtt_insert_sg_entries);
 
+dma_addr_t intel_gmch_gtt_read_entry(unsigned int pg,
+				     bool *is_present, bool *is_local)
+{
+	return intel_private.driver->read_entry(pg, is_present, is_local);
+}
+EXPORT_SYMBOL(intel_gmch_gtt_read_entry);
+
 #if IS_ENABLED(CONFIG_AGP_INTEL)
 static void intel_gmch_gtt_insert_pages(unsigned int first_entry,
 					unsigned int num_entries,
@@ -1126,6 +1160,19 @@ static void i965_write_entry(dma_addr_t addr,
 	writel_relaxed(addr | pte_flags, intel_private.gtt + entry);
 }
 
+static dma_addr_t i965_read_entry(unsigned int entry,
+				  bool *is_present, bool *is_local)
+{
+	u64 val;
+
+	val = readl(intel_private.gtt + entry);
+
+	*is_present = val & I810_PTE_VALID;
+	*is_local = false;
+
+	return ((val & 0xf0) << 28) | (val & ~0xfff);
+}
+
 static int i9xx_setup(void)
 {
 	phys_addr_t reg_addr;
@@ -1187,13 +1234,15 @@ static const struct intel_gtt_driver i81x_gtt_driver = {
 	.cleanup = i810_cleanup,
 	.check_flags = i830_check_flags,
 	.write_entry = i810_write_entry,
+	.read_entry = i810_read_entry,
 };
 static const struct intel_gtt_driver i8xx_gtt_driver = {
 	.gen = 2,
 	.has_pgtbl_enable = 1,
 	.setup = i830_setup,
 	.cleanup = i830_cleanup,
 	.write_entry = i830_write_entry,
+	.read_entry = i830_read_entry,
 	.dma_mask_size = 32,
 	.check_flags = i830_check_flags,
 	.chipset_flush = i830_chipset_flush,
@@ -1205,6 +1254,7 @@ static const struct intel_gtt_driver i915_gtt_driver = {
 	.cleanup = i9xx_cleanup,
 	/* i945 is the last gpu to need phys mem (for overlay and cursors). */
 	.write_entry = i830_write_entry,
+	.read_entry = i830_read_entry,
 	.dma_mask_size = 32,
 	.check_flags = i830_check_flags,
 	.chipset_flush = i9xx_chipset_flush,
@@ -1215,6 +1265,7 @@ static const struct intel_gtt_driver g33_gtt_driver = {
 	.setup = i9xx_setup,
 	.cleanup = i9xx_cleanup,
 	.write_entry = i965_write_entry,
+	.read_entry = i965_read_entry,
 	.dma_mask_size = 36,
 	.check_flags = i830_check_flags,
 	.chipset_flush = i9xx_chipset_flush,
@@ -1225,6 +1276,7 @@ static const struct intel_gtt_driver pineview_gtt_driver = {
 	.setup = i9xx_setup,
 	.cleanup = i9xx_cleanup,
 	.write_entry = i965_write_entry,
+	.read_entry = i965_read_entry,
 	.dma_mask_size = 36,
 	.check_flags = i830_check_flags,
 	.chipset_flush = i9xx_chipset_flush,
@@ -1235,6 +1287,7 @@ static const struct intel_gtt_driver i965_gtt_driver = {
 	.setup = i9xx_setup,
 	.cleanup = i9xx_cleanup,
 	.write_entry = i965_write_entry,
+	.read_entry = i965_read_entry,
 	.dma_mask_size = 36,
 	.check_flags = i830_check_flags,
 	.chipset_flush = i9xx_chipset_flush,
@@ -1244,6 +1297,7 @@ static const struct intel_gtt_driver g4x_gtt_driver = {
 	.setup = i9xx_setup,
 	.cleanup = i9xx_cleanup,
 	.write_entry = i965_write_entry,
+	.read_entry = i965_read_entry,
 	.dma_mask_size = 36,
 	.check_flags = i830_check_flags,
 	.chipset_flush = i9xx_chipset_flush,
@@ -1254,6 +1308,7 @@ static const struct intel_gtt_driver ironlake_gtt_driver = {
 	.setup = i9xx_setup,
 	.cleanup = i9xx_cleanup,
 	.write_entry = i965_write_entry,
+	.read_entry = i965_read_entry,
 	.dma_mask_size = 36,
 	.check_flags = i830_check_flags,
 	.chipset_flush = i9xx_chipset_flush,

include/drm/intel/intel-gtt.h

@@ -28,6 +28,8 @@ void intel_gmch_gtt_insert_sg_entries(struct sg_table *st,
 				      unsigned int pg_start,
 				      unsigned int flags);
 void intel_gmch_gtt_clear_range(unsigned int first_entry, unsigned int num_entries);
+dma_addr_t intel_gmch_gtt_read_entry(unsigned int pg,
+				     bool *is_present, bool *is_local);
 
 /* Special gtt memory types */
 #define AGP_DCACHE_MEMORY	1