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