diff options
Diffstat (limited to 'target/linux/pistachio/patches-4.9/105-spi-img-spfi-RX-maximum-burst-size-for-DMA-is-8.patch')
-rw-r--r-- | target/linux/pistachio/patches-4.9/105-spi-img-spfi-RX-maximum-burst-size-for-DMA-is-8.patch | 64 |
1 files changed, 64 insertions, 0 deletions
diff --git a/target/linux/pistachio/patches-4.9/105-spi-img-spfi-RX-maximum-burst-size-for-DMA-is-8.patch b/target/linux/pistachio/patches-4.9/105-spi-img-spfi-RX-maximum-burst-size-for-DMA-is-8.patch new file mode 100644 index 0000000000..47fcf3c0ba --- /dev/null +++ b/target/linux/pistachio/patches-4.9/105-spi-img-spfi-RX-maximum-burst-size-for-DMA-is-8.patch @@ -0,0 +1,64 @@ +From 56466f505f58f44b69feb7eaed3b506842800456 Mon Sep 17 00:00:00 2001 +From: Ionela Voinescu <ionela.voinescu@imgtec.com> +Date: Tue, 1 Mar 2016 17:49:45 +0000 +Subject: spi: img-spfi: RX maximum burst size for DMA is 8 + +The depth of the FIFOs is 16 bytes. The DMA request line is tied +to the half full/empty (depending on the use of the TX or RX FIFO) +threshold. For the TX FIFO, if you set a burst size of 8 (equal to +half the depth) the first burst goes into FIFO without any issues, +but due the latency involved (the time the data leaves the DMA +engine to the time it arrives at the FIFO), the DMA might trigger +another burst of 8. But given that there is no space for 2 additonal +bursts of 8, this would result in a failure. Therefore, we have to +keep the burst size for TX to 4 to accomodate for an extra burst. + +For the read (RX) scenario, the DMA request line goes high when +there is at least 8 entries in the FIFO (half full), and we can +program the burst size to be 8 because the risk of accidental burst +does not exist. The DMA engine will not trigger another read until +the read data for all the burst it has sent out has been received. + +While here, move the burst size setting outside of the if/else branches +as they have the same value for both 8 and 32 bit data widths. + +Signed-off-by: Ionela Voinescu <ionela.voinescu@imgtec.com> +--- + drivers/spi/spi-img-spfi.c | 6 ++---- + 1 file changed, 2 insertions(+), 4 deletions(-) + +diff --git a/drivers/spi/spi-img-spfi.c b/drivers/spi/spi-img-spfi.c +index 231b59c..8ad6c75 100644 +--- a/drivers/spi/spi-img-spfi.c ++++ b/drivers/spi/spi-img-spfi.c +@@ -346,12 +346,11 @@ static int img_spfi_start_dma(struct spi_master *master, + if (xfer->len % 4 == 0) { + rxconf.src_addr = spfi->phys + SPFI_RX_32BIT_VALID_DATA; + rxconf.src_addr_width = 4; +- rxconf.src_maxburst = 4; + } else { + rxconf.src_addr = spfi->phys + SPFI_RX_8BIT_VALID_DATA; + rxconf.src_addr_width = 1; +- rxconf.src_maxburst = 4; + } ++ rxconf.src_maxburst = 8; + dmaengine_slave_config(spfi->rx_ch, &rxconf); + + rxdesc = dmaengine_prep_slave_sg(spfi->rx_ch, xfer->rx_sg.sgl, +@@ -370,12 +369,11 @@ static int img_spfi_start_dma(struct spi_master *master, + if (xfer->len % 4 == 0) { + txconf.dst_addr = spfi->phys + SPFI_TX_32BIT_VALID_DATA; + txconf.dst_addr_width = 4; +- txconf.dst_maxburst = 4; + } else { + txconf.dst_addr = spfi->phys + SPFI_TX_8BIT_VALID_DATA; + txconf.dst_addr_width = 1; +- txconf.dst_maxburst = 4; + } ++ txconf.dst_maxburst = 4; + dmaengine_slave_config(spfi->tx_ch, &txconf); + + txdesc = dmaengine_prep_slave_sg(spfi->tx_ch, xfer->tx_sg.sgl, +-- +2.7.4 + |