From d9864228a2479e412d7e0d2221fe536f78329acd Mon Sep 17 00:00:00 2001 From: Aaron Durbin Date: Mon, 21 Jul 2014 22:11:29 -0500 Subject: [PATCH] tegra132: fix Rx FIFO underruns with slower SPI clock The SPI controller operates on packets which can be variable length up to 32-bit packets. It also has the ability to be put in packed or unpacked mode w.r.t each packet. i.e. does a single fifo register hold >= 1 packet. The current programming uses 8-bit packets in unpacked mode which means 4 fifo slots are used for a 32-bit DMA transfter. As the AHB can only operate on a minimum of 32-bit bursts the triggers need to be programmed correctly so that there is room for a full 32-bit DMA transaction. Previously faster SPI clocks just made things magically work. BUG=chrome-os-partner:30779 BRANCH=None TEST=Built and booted through coreboot with 20MHz SPI clock. Change-Id: I3f1cd4dddcea9514327b2363ed450a527db7e1fe Signed-off-by: Aaron Durbin Reviewed-on: https://chromium-review.googlesource.com/208862 Reviewed-by: Tom Warren Reviewed-by: Furquan Shaikh Commit-Queue: Furquan Shaikh --- src/soc/nvidia/tegra132/spi.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) diff --git a/src/soc/nvidia/tegra132/spi.c b/src/soc/nvidia/tegra132/spi.c index f1be207ced..973bdc94ea 100644 --- a/src/soc/nvidia/tegra132/spi.c +++ b/src/soc/nvidia/tegra132/spi.c @@ -530,10 +530,24 @@ static void tegra_spi_dma_start(struct tegra_spi_channel *spi) */ setbits_le32(&spi->regs->trans_status, SPI_STATUS_RDY); - if (spi->dma_out) + /* + * The DMA triggers have units of packets. As each packet is currently + * 1 byte the triggers need to be set to 4 packets (0b01) to match + * the AHB 32-bit (4 byte) tranfser. Otherwise the FIFO errors can + * occur. + */ + if (spi->dma_out) { + clrsetbits_le32(&spi->regs->dma_ctl, + SPI_DMA_CTL_TX_TRIG_MASK << SPI_DMA_CTL_TX_TRIG_SHIFT, + 1 << SPI_DMA_CTL_TX_TRIG_SHIFT); setbits_le32(&spi->regs->command1, SPI_CMD1_TX_EN); - if (spi->dma_in) + } + if (spi->dma_in) { + clrsetbits_le32(&spi->regs->dma_ctl, + SPI_DMA_CTL_RX_TRIG_MASK << SPI_DMA_CTL_RX_TRIG_SHIFT, + 1 << SPI_DMA_CTL_RX_TRIG_SHIFT); setbits_le32(&spi->regs->command1, SPI_CMD1_RX_EN); + } /* * To avoid underrun conditions, enable APB DMA before SPI DMA for