[U-Boot] [PATCH] Davinci: SPI performance enhancements

[Nick Thompson <nick.thompson@ge.com>]

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.