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Add DMA support to the MSIOF driver using platform data.
As MSIOF DMA is limited to 32-bit words (requiring byte/wordswapping for
smaller wordsizes), and the group length is limited to 256 words, DMA is
performed on two fixed pages, allocated and mapped at driver initialization
time.
Performance figures (in Mbps) on r8a7791/koelsch at different SPI clock
frequencies for 1024-byte and 4096-byte transfers:
1024 bytes 4096 bytes
- 3.25 MHz: PIO 2.1, DMA 2.6 | PIO 2.8, DMA 3.1
- 6.5 MHz: PIO 3.2, DMA 4.4 | PIO 5.0, DMA 5.9
- 13 MHz: PIO 4.2, DMA 6.6 | PIO 8.2, DMA 10.7
- 26 MHz: PIO 5.9, DMA 10.4 | PIO 12.4, DMA 18.4
Note that DMA is only faster than PIO for transfers that exceed the FIFO
size (typically 64 words / 256 bytes).
Also note that large transfers (larger than the group length for DMA, or
larger than the FIFO size for PIO), should use cs-gpio (with the
appropriate pinmux setup), as the hardware chipselect will be deasserted in
between chunks.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Mark Brown <broonie@linaro.org>
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This patch is V2 of SPI Master support for the SuperH MSIOF.
Full duplex, spi mode 0-3, active high cs, 3-wire and lsb
first should all be supported, but the driver has so far
only been tested with "mmc_spi".
The MSIOF hardware comes with 32-bit FIFOs for receive and
transmit, and this driver simply breaks the SPI messages
into FIFO-sized chunks. The MSIOF hardware manages the pins
for clock, receive and transmit (sck/miso/mosi), but the chip
select pin is managed by software and must be configured as
a regular GPIO pin by the board code.
Performance wise there is still room for improvement, but
on a Ecovec board with the built-in sh7724 MSIOF0 this driver
gets Mini-sd read speeds of about half a megabyte per second.
Future work include better clock setup and merging of 8-bit
transfers into 32-bit words to reduce interrupt load and
improve throughput.
Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
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