bus: mhi: pci-generic: configurable network interface MRU

The MRU value used by the MHI MBIM network interface affects
the throughput performance of the interface. Different modem
models use different default MRU sizes based on their bandwidth
capabilities. Large values generally result in higher throughput
for larger packet sizes.

In addition if the MRU used by the MHI device is larger than that
specified in the MHI net device the data is fragmented and needs
to be re-assembled which generates a (single) warning message about
the fragmented packets. Setting the MRU on both ends avoids the
extra processing to re-assemble the packets.

This patch allows the documented MRU for a modem to be automatically
set as the MHI net device MRU avoiding fragmentation and improving
throughput performance.
Signed-off-by: Richard Laing <richard.laing@alliedtelesis.co.nz>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/bus/mhi/pci_generic.c

@@ -32,6 +32,7 @@
  * @edl: emergency download mode firmware path (if any)
  * @bar_num: PCI base address register to use for MHI MMIO register space
  * @dma_data_width: DMA transfer word size (32 or 64 bits)
+ * @mru_default: default MRU size for MBIM network packets
  */
 struct mhi_pci_dev_info {
 	const struct mhi_controller_config *config;
@@ -40,6 +41,7 @@ struct mhi_pci_dev_info {
 	const char *edl;
 	unsigned int bar_num;
 	unsigned int dma_data_width;
+	unsigned int mru_default;
 };
 
 #define MHI_CHANNEL_CONFIG_UL(ch_num, ch_name, el_count, ev_ring) \
@@ -251,7 +253,8 @@ static const struct mhi_pci_dev_info mhi_qcom_sdx55_info = {
 	.edl = "qcom/sdx55m/edl.mbn",
 	.config = &modem_qcom_v1_mhiv_config,
 	.bar_num = MHI_PCI_DEFAULT_BAR_NUM,
-	.dma_data_width = 32
+	.dma_data_width = 32,
+	.mru_default = 32768
 };
 
 static const struct mhi_pci_dev_info mhi_qcom_sdx24_info = {
@@ -643,6 +646,7 @@ static int mhi_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 	mhi_cntrl->wake_get = mhi_pci_wake_get_nop;
 	mhi_cntrl->wake_put = mhi_pci_wake_put_nop;
 	mhi_cntrl->wake_toggle = mhi_pci_wake_toggle_nop;
+	mhi_cntrl->mru = info->mru_default;
 
 	err = mhi_pci_claim(mhi_cntrl, info->bar_num, DMA_BIT_MASK(info->dma_data_width));
 	if (err)

drivers/net/mhi/net.c

@@ -329,6 +329,7 @@ static int mhi_net_newlink(void *ctxt, struct net_device *ndev, u32 if_id,
 	mhi_netdev->mdev = mhi_dev;
 	mhi_netdev->skbagg_head = NULL;
 	mhi_netdev->proto = info->proto;
+	mhi_netdev->mru = mhi_dev->mhi_cntrl->mru;
 
 	INIT_DELAYED_WORK(&mhi_netdev->rx_refill, mhi_net_rx_refill_work);
 	u64_stats_init(&mhi_netdev->stats.rx_syncp);

drivers/net/mhi/proto_mbim.c

@@ -292,7 +292,9 @@ static int mbim_init(struct mhi_net_dev *mhi_netdev)
 
 	ndev->needed_headroom = sizeof(struct mbim_tx_hdr);
 	ndev->mtu = MHI_MBIM_DEFAULT_MTU;
-	mhi_netdev->mru = MHI_MBIM_DEFAULT_MRU;
+
+	if (!mhi_netdev->mru)
+		mhi_netdev->mru = MHI_MBIM_DEFAULT_MRU;
 
 	return 0;
 }

include/linux/mhi.h

@@ -356,6 +356,7 @@ struct mhi_controller_config {
  * @fbc_download: MHI host needs to do complete image transfer (optional)
  * @wake_set: Device wakeup set flag
  * @irq_flags: irq flags passed to request_irq (optional)
+ * @mru: the default MRU for the MHI device
  *
  * Fields marked as (required) need to be populated by the controller driver
  * before calling mhi_register_controller(). For the fields marked as (optional)
@@ -448,6 +449,7 @@ struct mhi_controller {
 	bool fbc_download;
 	bool wake_set;
 	unsigned long irq_flags;
+	u32 mru;
 };
 
 /**