net: mana: Fall back to scattered pages for GDMA queues

Each GDMA queue ring is one dma_alloc_coherent() of the whole ring size.
Such high-order allocations fail first under memory fragmentation, so
queue setup can fail with memory still free.

The hardware does not need the ring physically contiguous:
mana_gd_create_dma_region() already maps it as a list of MANA_PAGE_SIZE
(4K) device addresses. Only the driver's linear CPU view needs
contiguity, and it goes through mana_gd_ring_ptr() and
mana_gd_ring_contig_avail(); change both to map offsets onto
scattered pages.

Add a fallback in mana_gd_alloc_memory(): data-path queues pass
allow_scatter=true, so when the contiguous allocation fails the ring is
backed by a vector of scattered PAGE_SIZE (order-0) coherent pages,
presenting the same DMA page-list layout to the device. The HW channel
bootstrap keeps allow_scatter=false, and the debugfs ring dumper reads
scattered rings through the same helpers.

Signed-off-by: Aditya Garg <gargaditya@linux.microsoft.com>
Link: https://patch.msgid.link/20260807210002.1695263-3-gargaditya@linux.microsoft.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

1 files changed, 17 insertions, 2 deletions

diff --git a/include/net/mana/gdma.h b/include/net/mana/gdma.h
index 70a7f1fee5d3..9d57a0ea0e5e 100644
--- a/include/net/mana/gdma.h
+++ b/include/net/mana/gdma.h
@@ -241,6 +241,14 @@ struct gdma_mem_info {
 	void *virt_addr;
 	u64 length;
 
+	/* Scattered fallback: when @nr_pages > 0 the ring is that many
+	 * PAGE_SIZE coherent allocations in @pages_va/@pages_dma, not
+	 * @virt_addr/@dma_handle.
+	 */
+	void **pages_va;
+	dma_addr_t *pages_dma;
+	unsigned int nr_pages;
+
 	/* Allocated by the PF driver */
 	u64 dma_region_handle;
 };
@@ -516,6 +524,9 @@ int mana_gd_poll_cq(struct gdma_queue *cq, struct gdma_comp *comp, int num_cqe);
 
 void mana_gd_ring_cq(struct gdma_queue *cq, u8 arm_bit);
 
+ssize_t mana_gd_read_ring(struct gdma_queue *q, char __user *buf,
+			  size_t count, loff_t *pos);
+
 int mana_schedule_serv_work(struct gdma_context *gc, enum gdma_eqe_type type);
 
 void mana_gd_ring_dim(struct gdma_queue *cq, u32 mod_usec, bool mod_usec_vld,
@@ -672,6 +683,9 @@ enum {
 /* Driver supports dynamic interrupt moderation - DIM */
 #define GDMA_DRV_CAP_FLAG_1_DYN_INTERRUPT_MODERATION BIT(28)
 
+/* Driver supports non-contiguous queue buffers */
+#define GDMA_DRV_CAP_FLAG_1_NON_CONTIGUOUS_BUFFERS BIT(30)
+
 #define GDMA_DRV_CAP_FLAGS1 \
 	(GDMA_DRV_CAP_FLAG_1_EQ_SHARING_MULTI_VPORT | \
 	 GDMA_DRV_CAP_FLAG_1_NAPI_WKDONE_FIX | \
@@ -688,7 +702,8 @@ enum {
 	 GDMA_DRV_CAP_FLAG_1_HANDLE_STALL_SQ_RECOVERY | \
 	 GDMA_DRV_CAP_FLAG_1_HWC_TIMEOUT_RECOVERY | \
 	 GDMA_DRV_CAP_FLAG_1_EQ_MSI_UNSHARE_MULTI_VPORT | \
-	 GDMA_DRV_CAP_FLAG_1_DYN_INTERRUPT_MODERATION)
+	 GDMA_DRV_CAP_FLAG_1_DYN_INTERRUPT_MODERATION | \
+	 GDMA_DRV_CAP_FLAG_1_NON_CONTIGUOUS_BUFFERS)
 
 #define GDMA_DRV_CAP_FLAGS2 0
 
@@ -1049,7 +1064,7 @@ void mana_gd_wq_ring_doorbell(struct gdma_context *gc,
 			      struct gdma_queue *queue);
 
 int mana_gd_alloc_memory(struct gdma_context *gc, unsigned int length,
-			 struct gdma_mem_info *gmi);
+			 struct gdma_mem_info *gmi, bool allow_scatter);
 
 void mana_gd_free_memory(struct gdma_mem_info *gmi);