usb: musb: cppi41: fix not transmitting zero length packet issue

CPPI TX does not transmit ZLP for TX transfers which
- transfer size is multiple of EP packet size,
- and URB_ZERO_PACKET is set in urb->transfer_flags.

The fix is transmitting the ZLP using PIO mode after the CPPI TX is
done.

Validated using the following usbtest write case in MUSB host mode.

  # testusb -t1 -c1

Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

1 files changed, 15 insertions, 2 deletions

diff --git a/drivers/usb/musb/musb_cppi41.c b/drivers/usb/musb/musb_cppi41.c
index 47ae6455d073..3ee133f675ab 100644
--- a/drivers/usb/musb/musb_cppi41.c
+++ b/drivers/usb/musb/musb_cppi41.c
@@ -39,6 +39,7 @@ struct cppi41_dma_channel {
         u32 transferred;
         u32 packet_sz;
         struct list_head tx_check;
+        int tx_zlp;
 };
 
 #define MUSB_DMA_NUM_CHANNELS 15
@@ -122,6 +123,8 @@ static void cppi41_trans_done(struct cppi41_dma_channel *cppi41_channel)
 {
         struct musb_hw_ep *hw_ep = cppi41_channel->hw_ep;
         struct musb *musb = hw_ep->musb;
+        void __iomem *epio = hw_ep->regs;
+        u16 csr;
 
         if (!cppi41_channel->prog_len ||
             (cppi41_channel->channel.status == MUSB_DMA_STATUS_FREE)) {
@@ -131,15 +134,24 @@ static void cppi41_trans_done(struct cppi41_dma_channel *cppi41_channel)
                         cppi41_channel->transferred;
                 cppi41_channel->channel.status = MUSB_DMA_STATUS_FREE;
                 cppi41_channel->channel.rx_packet_done = true;
+
+                /*
+                 * transmit ZLP using PIO mode for transfers which size is
+                 * multiple of EP packet size.
+                 */
+                if (cppi41_channel->tx_zlp && (cppi41_channel->transferred %
+                                        cppi41_channel->packet_sz) == 0) {
+                        musb_ep_select(musb->mregs, hw_ep->epnum);
+                        csr = MUSB_TXCSR_MODE | MUSB_TXCSR_TXPKTRDY;
+                        musb_writew(epio, MUSB_TXCSR, csr);
+                }
                 musb_dma_completion(musb, hw_ep->epnum, cppi41_channel->is_tx);
         } else {
                 /* next iteration, reload */
                 struct dma_chan *dc = cppi41_channel->dc;
                 struct dma_async_tx_descriptor *dma_desc;
                 enum dma_transfer_direction direction;
-                u16 csr;
                 u32 remain_bytes;
-                void __iomem *epio = cppi41_channel->hw_ep->regs;
 
                 cppi41_channel->buf_addr += cppi41_channel->packet_sz;
 
@@ -363,6 +375,7 @@ static bool cppi41_configure_channel(struct dma_channel *channel,
         cppi41_channel->total_len = len;
         cppi41_channel->transferred = 0;
         cppi41_channel->packet_sz = packet_sz;
+        cppi41_channel->tx_zlp = (cppi41_channel->is_tx && mode) ? 1 : 0;
 
         /*
          * Due to AM335x' Advisory 1.0.13 we are not allowed to transfer more