eth: fbnic: Account for page fragments when updating BDQ tail

FBNIC supports fixed size buffers of 4K. When PAGE_SIZE > 4K, we
fragment the page across multiple descriptors (FBNIC_BD_FRAG_COUNT).
When refilling the BDQ, the correct number of entries are populated,
but tail was only incremented by one. So on a system with 64K pages,
HW would get one descriptor refilled for every 16 we populate.

Additionally, we program the ring size in the HW when enabling the BDQ.
This was not accounting for page fragments, so on systems with 64K pages,
the HW used 1/16th of the ring.

Fixes: 0cb4c0a ("eth: fbnic: Implement Rx queue alloc/start/stop/free")
Signed-off-by: Dimitri Daskalakis <daskald@meta.com>
Link: https://patch.msgid.link/20260324195123.3486219-2-dimitri.daskalakis1@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: ddaskala

drivers/net/ethernet/meta/fbnic/fbnic_txrx.c

@@ -927,7 +927,7 @@ static void fbnic_fill_bdq(struct fbnic_ring *bdq)
 		/* Force DMA writes to flush before writing to tail */
 		dma_wmb();
 
-		writel(i, bdq->doorbell);
+		writel(i * FBNIC_BD_FRAG_COUNT, bdq->doorbell);
 	}
 }
 
@@ -2564,7 +2564,7 @@ static void fbnic_enable_bdq(struct fbnic_ring *hpq, struct fbnic_ring *ppq)
 	hpq->tail = 0;
 	hpq->head = 0;
 
-	log_size = fls(hpq->size_mask);
+	log_size = fls(hpq->size_mask) + ilog2(FBNIC_BD_FRAG_COUNT);
 
 	/* Store descriptor ring address and size */
 	fbnic_ring_wr32(hpq, FBNIC_QUEUE_BDQ_HPQ_BAL, lower_32_bits(hpq->dma));
@@ -2576,7 +2576,7 @@ static void fbnic_enable_bdq(struct fbnic_ring *hpq, struct fbnic_ring *ppq)
 	if (!ppq->size_mask)
 		goto write_ctl;
 
-	log_size = fls(ppq->size_mask);
+	log_size = fls(ppq->size_mask) + ilog2(FBNIC_BD_FRAG_COUNT);
 
 	/* Add enabling of PPQ to BDQ control */
 	bdq_ctl |= FBNIC_QUEUE_BDQ_CTL_PPQ_ENABLE;