On 22/06/10 16:27, Paulraj, Sandeep wrote:
The following restructuring and optimisations increase the SPI read performance from 1.3MiB/s (on da850) to 2.87MiB/s (on da830):
Remove continual revaluation of driver state from the core of the copy loop. State can not change during the copy loop, so it is possible to move these evaluations to before the copy loop.
Cost is more code space as loop variants are required for each set of possible configurations. The loops are simpler however, so the extra is only 128bytes on da830 with CONFIG_SPI_HALF_DUPLEX defined.
Unrolling the first copy loop iteration allows the TX buffer to be pre-loaded reducing SPI clock starvation.
Unrolling the last copy loop iteration removes testing for the final loop iteration every time round the loop.
Using the RX buffer empty flag as a transfer throttle allows the assumption that it is always safe to write to the TX buffer, so polling of TX buffer full flag can be removed.
Signed-off-by: Nick Thompson nick.thompson@ge.com
da850 and da830 are similar devices. The SPI module is common to both, but da850 uses DDR and da830 uses SDRAM. The EVM's might not actually be comparable, but they appear to be at least similar.
The speed was tested with a 8MiB transfer from SPI FLASH using:
sf read 0xc0008000 0 0x800000
drivers/spi/davinci_spi.c | 195 +++++++++++++++++++++++++++++-----------
Applied to u-boot-ti/next
Sandeep,
You're too quick for me :-) I was going to do a v2 patch to cover a couple of Delio's points. They are not critical issues though, so I think we can let the pull request go through and I will submit a new patch once it hits u-boot/next:
On 21/06/10 19:38, Delio Brignoli wrote:
- if (!dout)
return davinci_spi_read(slave, len, din, flags);- else if (!din)
return davinci_spi_write(slave, len, dout, flags);+#ifndef CONFIG_SPI_HALF_DUPLEX
- else
return davinci_spi_read_write(slave, len, din, dout, flags);+#endif
I think there should always be an else branch at the end even if CONFIG_SPI_HALF_DUPLEX is not defined. Something like:
#else flags |= SPI_XFER_END; #endif
to terminate the transfer instead of failing silently. In fact it should signal the error condition somehow, but I do not know enough about u-boot to provide an advice on this.
Its a non issue if the driver is called correctly in the first place, but we can't be sure of that.
Nick.