target/linux/bcm27xx/patches-6.1/950-1073-spi-dw-dma-Get-the-last-DMA-scoop-out-of-the-FIFO.patch

   1 From 686fe776309fba5cad642c40177d39bf1fb320b2 Mon Sep 17 00:00:00 2001
   2 From: Phil Elwell <phil@raspberrypi.com>
   3 Date: Tue, 7 Nov 2023 14:49:47 +0000
   4 Subject: [PATCH] spi: dw-dma: Get the last DMA scoop out of the FIFO
   5
   6 With a DMA FIFO threshold greater than 1 (encoded as 0), it is possible
   7 for data in the FIFO to be inaccessible, causing the transfer to fail
   8 after a timeout. If the transfer includes a transmission, reduce the
   9 RX threshold when the TX completes, otherwise use 1 for the whole
  10 transfer (inefficient, but not catastrophic at SPI data rates).
  11
  12 See: https://github.com/raspberrypi/linux/issues/5696
  13
  14 Signed-off-by: Phil Elwell <phil@raspberrypi.com>
  15 ---
  16  drivers/spi/spi-dw-dma.c | 6 +++++-
  17  1 file changed, 5 insertions(+), 1 deletion(-)
  18
  19 --- a/drivers/spi/spi-dw-dma.c
  20 +++ b/drivers/spi/spi-dw-dma.c
  21 @@ -275,8 +275,10 @@ static void dw_spi_dma_tx_done(void *arg
  22         struct dw_spi *dws = arg;
  23
  24         clear_bit(DW_SPI_TX_BUSY, &dws->dma_chan_busy);
  25 -       if (test_bit(DW_SPI_RX_BUSY, &dws->dma_chan_busy))
  26 +       if (test_bit(DW_SPI_RX_BUSY, &dws->dma_chan_busy)) {
  27 +               dw_writel(dws, DW_SPI_DMARDLR, 0);
  28                 return;
  29 +       }
  30
  31         complete(&dws->dma_completion);
  32  }
  33 @@ -602,6 +604,8 @@ static int dw_spi_dma_transfer(struct dw
  34
  35         nents = max(xfer->tx_sg.nents, xfer->rx_sg.nents);
  36
  37 +       dw_writel(dws, DW_SPI_DMARDLR, xfer->tx_buf ? (dws->rxburst - 1) : 0);
  38 +
  39         /*
  40          * Execute normal DMA-based transfer (which submits the Rx and Tx SG
  41          * lists directly to the DMA engine at once) if either full hardware