[U-Boot] [PATCH V2] spi: exynos: Minimise access to SPI FIFO level

[Jagan Teki]

Hi,

On Thu, Jun 13, 2013 at 1:29 AM, Jagan Teki <jagannadh.teki at gmail.com> wrote:
> On 30-05-2013 10:57, Rajeshwari Shinde wrote:
>>
>> Accessing SPI registers is slow, but access to the FIFO level register
>> in particular seems to be extraordinarily expensive (I measure up to
>> 600ns). Perhaps it is required to synchronise with the SPI byte output
>> logic which might run at 1/8th of the 40MHz SPI speed (just a guess).
>>
>> Reduce access to this register by filling up and emptying FIFOs
>> more completely, rather than just one word each time around the inner
>> loop.
>>
>> Since the rxfifo value will now likely be much greater that what we read
>> before we fill the txfifo, we only fill the txfifo halfway. This is
>> because if the txfifo is empty, but the rxfifo has data in it, then
>> writing
>> too much data to the txfifo may overflow the rxfifo as data arrives.
>>
>> This speeds up SPI flash reading from about 1MB/s to about 2MB/s on snow.
>>
>> Based on "[PATCH 0/2 V3] exynos: Support a delay after deactivate for SPI"
>
>
> Please use the format i suggested on earlier patch
> http://patchwork.ozlabs.org/patch/247451/
>
> Thanks,
> Jagan.
>
>>
>> Signed-off-by: Simon Glass <sjg at chromium.org>
>> Signed-off-by: Rajeshwari Shinde <rajeshwari.s at samsung.com>
>> ---
>> Changes in V2:
>>         - Rebased on "[PATCH 0/2 V5] spi: Enable SPI_PREAMBLE Mode"
>>   drivers/spi/exynos_spi.c |   27 +++++++++++++++------------
>>   1 files changed, 15 insertions(+), 12 deletions(-)
>>
>> diff --git a/drivers/spi/exynos_spi.c b/drivers/spi/exynos_spi.c
>> index deb32bd..bcca3d6 100644
>> --- a/drivers/spi/exynos_spi.c
>> +++ b/drivers/spi/exynos_spi.c
>> @@ -259,24 +259,27 @@ static int spi_rx_tx(struct exynos_spi_slave
>> *spi_slave, int todo,
>>
>>                 /* Keep the fifos full/empty. */
>>                 spi_get_fifo_levels(regs, &rx_lvl, &tx_lvl);
>> -               if (tx_lvl < spi_slave->fifo_size && out_bytes) {
>> +               while (tx_lvl < spi_slave->fifo_size/2 && out_bytes) {
>>                         temp = txp ? *txp++ : 0xff;
>>                         writel(temp, &regs->tx_data);
>>                         out_bytes--;
>> +                       tx_lvl++;
>>                 }
>>                 if (rx_lvl > 0) {
>> -                       temp = readl(&regs->rx_data);
>> -                       if (spi_slave->skip_preamble) {
>> -                               if (temp == SPI_PREAMBLE_END_BYTE) {
>> -                                       spi_slave->skip_preamble = 0;
>> -                                       stopping = 0;
>> +                       while (rx_lvl > 0) {
>> +                               temp = readl(&regs->rx_data);
>> +                               if (spi_slave->skip_preamble) {
>> +                                       if (temp == SPI_PREAMBLE_END_BYTE)
>> {
>> +                                               spi_slave->skip_preamble =
>> 0;
>> +                                               stopping = 0;
>> +                                       }
>> +                               } else {
>> +                                       if (rxp || stopping)
>> +                                               *rxp++ = temp;
>> +                                       in_bytes--;
>>                                 }
>> -                       } else {
>> -                               if (rxp || stopping)
>> -                                       *rxp++ = temp;
>> -                               in_bytes--;
>> -                       }
>> -                       toread--;
>> +                               toread--;
>> +                               rx_lvl--;
>>                 } else if (!toread) {
>>                         /*
>>                          * We have run out of input data, but haven't read
>>
>

Any plan to send this patch?
Please send by fixing few comments on last review.

Also see the patches in:
http://patchwork.ozlabs.org/patch/247457/
http://patchwork.ozlabs.org/patch/247461/

Please let me know for any concerns.

--
Thanks,
Jagan.