iwlwifi: pcie: remove TR/CR tail allocations

The TR/CR tail data are meant to be per-queue-arrays, however,
we allocate them completely wrong (we have a separate allocation
per queue).

Looking at this more closely, it turns out that the hardware
never uses these - we have a separate free list per RX queue
and maintain a write pointer for that in a register, and the
RX itself is indicated in the RB status (rb_stts) DMA region.

Despite nothing using the tail pointers, the hardware will
unconditionally access them to write updates, even when we aren't
using CRs/TRs.

Give it dummy values that we never use/update so it can do that
without causing trouble.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20210617110647.5f5764e04c46.I4d5de1929be048085767f1234a1e07b517ab6a2d@changeidSigned-off-by: Luca Coelho <luciano.coelho@intel.com>

drivers/net/wireless/intel/iwlwifi/pcie/ctxt-info-gen3.c

@@ -138,8 +138,15 @@ int iwl_pcie_ctxt_info_gen3_init(struct iwl_trans *trans,
 
 	/* Allocate prph information
 	 * currently we don't assign to the prph info anything, but it would get
-	 * assigned later */
-	prph_info = dma_alloc_coherent(trans->dev, sizeof(*prph_info),
+	 * assigned later
+	 *
+	 * We also use the second half of this page to give the device some
+	 * dummy TR/CR tail pointers - which shouldn't be necessary as we don't
+	 * use this, but the hardware still reads/writes there and we can't let
+	 * it go do that with a NULL pointer.
+	 */
+	BUILD_BUG_ON(sizeof(*prph_info) > PAGE_SIZE / 2);
+	prph_info = dma_alloc_coherent(trans->dev, PAGE_SIZE,
 				       &trans_pcie->prph_info_dma_addr,
 				       GFP_KERNEL);
 	if (!prph_info) {
@@ -166,13 +173,9 @@ int iwl_pcie_ctxt_info_gen3_init(struct iwl_trans *trans,
 	ctxt_info_gen3->cr_head_idx_arr_base_addr =
 		cpu_to_le64(trans_pcie->rxq->rb_stts_dma);
 	ctxt_info_gen3->tr_tail_idx_arr_base_addr =
-		cpu_to_le64(trans_pcie->rxq->tr_tail_dma);
+		cpu_to_le64(trans_pcie->prph_info_dma_addr + PAGE_SIZE / 2);
 	ctxt_info_gen3->cr_tail_idx_arr_base_addr =
-		cpu_to_le64(trans_pcie->rxq->cr_tail_dma);
-	ctxt_info_gen3->cr_idx_arr_size =
-		cpu_to_le16(IWL_NUM_OF_COMPLETION_RINGS);
-	ctxt_info_gen3->tr_idx_arr_size =
-		cpu_to_le16(IWL_NUM_OF_TRANSFER_RINGS);
+		cpu_to_le64(trans_pcie->prph_info_dma_addr + 3 * PAGE_SIZE / 4);
 	ctxt_info_gen3->mtr_base_addr =
 		cpu_to_le64(trans->txqs.txq[trans->txqs.cmd.q_id]->dma_addr);
 	ctxt_info_gen3->mcr_base_addr =
@@ -216,9 +219,7 @@ int iwl_pcie_ctxt_info_gen3_init(struct iwl_trans *trans,
 			  trans_pcie->ctxt_info_dma_addr);
 	trans_pcie->ctxt_info_gen3 = NULL;
 err_free_prph_info:
-	dma_free_coherent(trans->dev,
-			  sizeof(*prph_info),
-			prph_info,
+	dma_free_coherent(trans->dev, PAGE_SIZE, prph_info,
 			  trans_pcie->prph_info_dma_addr);
 
 err_free_prph_scratch:
@@ -251,8 +252,7 @@ void iwl_pcie_ctxt_info_gen3_free(struct iwl_trans *trans)
 	trans_pcie->prph_scratch_dma_addr = 0;
 	trans_pcie->prph_scratch = NULL;
 
-	dma_free_coherent(trans->dev, sizeof(*trans_pcie->prph_info),
-			  trans_pcie->prph_info,
+	dma_free_coherent(trans->dev, PAGE_SIZE, trans_pcie->prph_info,
 			  trans_pcie->prph_info_dma_addr);
 	trans_pcie->prph_info_dma_addr = 0;
 	trans_pcie->prph_info = NULL;

drivers/net/wireless/intel/iwlwifi/pcie/internal.h

@@ -111,10 +111,6 @@ struct iwl_rx_completion_desc {
  * @bd_dma: bus address of buffer of receive buffer descriptors (rbd)
  * @used_bd: driver's pointer to buffer of used receive buffer descriptors (rbd)
  * @used_bd_dma: physical address of buffer of used receive buffer descriptors (rbd)
- * @tr_tail: driver's pointer to the transmission ring tail buffer
- * @tr_tail_dma: physical address of the buffer for the transmission ring tail
- * @cr_tail: driver's pointer to the completion ring tail buffer
- * @cr_tail_dma: physical address of the buffer for the completion ring tail
  * @read: Shared index to newest available Rx buffer
  * @write: Shared index to oldest written Rx packet
  * @free_count: Number of pre-allocated buffers in rx_free
@@ -142,10 +138,6 @@ struct iwl_rxq {
 		struct iwl_rx_completion_desc *cd;
 	};
 	dma_addr_t used_bd_dma;
-	__le16 *tr_tail;
-	dma_addr_t tr_tail_dma;
-	__le16 *cr_tail;
-	dma_addr_t cr_tail_dma;
 	u32 read;
 	u32 write;
 	u32 free_count;
@@ -533,9 +525,6 @@ static inline void _iwl_disable_interrupts(struct iwl_trans *trans)
 	IWL_DEBUG_ISR(trans, "Disabled interrupts\n");
 }
 
-#define IWL_NUM_OF_COMPLETION_RINGS	31
-#define IWL_NUM_OF_TRANSFER_RINGS	527
-
 static inline int iwl_pcie_get_num_sections(const struct fw_img *fw,
 					    int start)
 {

drivers/net/wireless/intel/iwlwifi/pcie/rx.c

@@ -663,7 +663,6 @@ static int iwl_pcie_free_bd_size(struct iwl_trans *trans, bool use_rx_td)
 static void iwl_pcie_free_rxq_dma(struct iwl_trans *trans,
 				  struct iwl_rxq *rxq)
 {
-	struct device *dev = trans->dev;
 	bool use_rx_td = (trans->trans_cfg->device_family >=
 			  IWL_DEVICE_FAMILY_AX210);
 	int free_size = iwl_pcie_free_bd_size(trans, use_rx_td);
@@ -685,21 +684,6 @@ static void iwl_pcie_free_rxq_dma(struct iwl_trans *trans,
 				  rxq->used_bd, rxq->used_bd_dma);
 	rxq->used_bd_dma = 0;
 	rxq->used_bd = NULL;
-
-	if (trans->trans_cfg->device_family < IWL_DEVICE_FAMILY_AX210)
-		return;
-
-	if (rxq->tr_tail)
-		dma_free_coherent(dev, sizeof(__le16),
-				  rxq->tr_tail, rxq->tr_tail_dma);
-	rxq->tr_tail_dma = 0;
-	rxq->tr_tail = NULL;
-
-	if (rxq->cr_tail)
-		dma_free_coherent(dev, sizeof(__le16),
-				  rxq->cr_tail, rxq->cr_tail_dma);
-	rxq->cr_tail_dma = 0;
-	rxq->cr_tail = NULL;
 }
 
 static int iwl_pcie_alloc_rxq_dma(struct iwl_trans *trans,
@@ -744,21 +728,6 @@ static int iwl_pcie_alloc_rxq_dma(struct iwl_trans *trans,
 	rxq->rb_stts_dma =
 		trans_pcie->base_rb_stts_dma + rxq->id * rb_stts_size;
 
-	if (!use_rx_td)
-		return 0;
-
-	/* Allocate the driver's pointer to TR tail */
-	rxq->tr_tail = dma_alloc_coherent(dev, sizeof(__le16),
-					  &rxq->tr_tail_dma, GFP_KERNEL);
-	if (!rxq->tr_tail)
-		goto err;
-
-	/* Allocate the driver's pointer to CR tail */
-	rxq->cr_tail = dma_alloc_coherent(dev, sizeof(__le16),
-					  &rxq->cr_tail_dma, GFP_KERNEL);
-	if (!rxq->cr_tail)
-		goto err;
-
 	return 0;
 
 err:
@@ -1590,9 +1559,6 @@ static int iwl_pcie_rx_handle(struct iwl_trans *trans, int queue, int budget)
 out:
 	/* Backtrack one entry */
 	rxq->read = i;
-	/* update cr tail with the rxq read pointer */
-	if (trans->trans_cfg->device_family >= IWL_DEVICE_FAMILY_AX210)
-		*rxq->cr_tail = cpu_to_le16(r);
 	spin_unlock(&rxq->lock);
 
 	/*