linux-kernel - [PATCH 6/7] PCI: epf-mhi: Use iATU for small transfers

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Date:   Tue,  6 Jun 2023 17:28:13 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     lpieralisi@...nel.org, kw@...ux.com
Cc:     kishon@...nel.org, bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Subject: [PATCH 6/7] PCI: epf-mhi: Use iATU for small transfers

For transfers below 4K, let's use iATU since using eDMA for such small
transfers is not efficient. This is mainly due to the fact that setting
up a eDMA transfer and waiting for its completion adds some latency. This
latency is negligible for large transfers but not for the smaller ones.

With this hack, there is an increase in ~50Mbps throughput on both MHI UL
(Uplink) and DL (Downlink) channels.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
---
 drivers/pci/endpoint/functions/pci-epf-mhi.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/pci/endpoint/functions/pci-epf-mhi.c b/drivers/pci/endpoint/functions/pci-epf-mhi.c
index f4d1d60bde56..94cf68bdd235 100644
--- a/drivers/pci/endpoint/functions/pci-epf-mhi.c
+++ b/drivers/pci/endpoint/functions/pci-epf-mhi.c
@@ -288,6 +288,9 @@ static int pci_epf_mhi_edma_read(struct mhi_ep_cntrl *mhi_cntrl, u64 from,
 	dma_addr_t dst_addr;
 	int ret;
 
+	if (size < SZ_4K)
+		return pci_epf_mhi_iatu_read(mhi_cntrl, from, to, size);
+
 	mutex_lock(&epf_mhi->lock);
 
 	config.direction = DMA_DEV_TO_MEM;
@@ -354,6 +357,9 @@ static int pci_epf_mhi_edma_write(struct mhi_ep_cntrl *mhi_cntrl, void *from,
 	dma_addr_t src_addr;
 	int ret;
 
+	if (size < SZ_4K)
+		return pci_epf_mhi_iatu_write(mhi_cntrl, from, to, size);
+
 	mutex_lock(&epf_mhi->lock);
 
 	config.direction = DMA_MEM_TO_DEV;
-- 
2.25.1