Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1295585

Re: [PATCH v5 2/2] spi: sun4i: Add support for wait time between word transmissions

Show all headers | View raw

Hi,

2015-12-18 12:16 GMT+01:00 Maxime Ripard <maxime.ripard@free-electrons.com>:

>>       sun4i_spi_write(sspi, SUN4I_CLK_CTL_REG, reg);
>>
>> +     /*
>> +      * Setup wait time between words.
>> +      *
>> +      * Wait time is set in SPI_CLK cycles. The SPI hardware needs 3
>> +      * additional cycles to setup the wait counter, so the minimum delay
>> +      * time is 4 cycles.
>> +      */
>> +     if (spi->word_wait_ns) {
>> +             clk_ns = DIV_ROUND_UP(1000000000, tfr->speed_hz);
>
> You should use the actual rate of the clock returned by clk_get_rate
> (or probably just use mclk_rate).
>
> The clock driver might round the frequency to something else than what
> was set in clk_set_rate, which would make your calculation here a bit
> off.

Yes, good point! And as the wait clock counter is based on the actual
SPI_CLK and not the mod clock, I need to calculate the exact clock
myself before handling the wait clock setting. Will amend the patch
and send a new version.

While looking into this, I also noticed a problem with a previous
patch of mine, which changed the spi-sun[46]i to use
transfer->speed_hz instead of the spi->max_speed_hz: I also changed
the mclk_rate calculation to be based on tfr->speed_hz, which should
have stayed with spi->max_speed_hz. In the current state, the clock
calculations only ever increase mclk_rate, wich leads to very
different clocks being set depending on which clock was used on the
previous transfer. Will send a fix for that as well in a separate
patch.

Cheers,

   Marcus
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

[PATCH v5 0/2] spi: dts: sun4i: Add support for wait time between word transmissions Marcus Weseloh <mweseloh42@gmail.com> - 2015-12-17 12:50 +0100
  [PATCH v5 1/2] spi: dts: Add new device property to specifcy a wait time between word transmissions Marcus Weseloh <mweseloh42@gmail.com> - 2015-12-17 12:50 +0100
    Re: [PATCH v5 1/2] spi: dts: Add new device property to specifcy a  wait time between word transmissions Maxime Ripard <maxime.ripard@free-electrons.com> - 2015-12-18 21:50 +0100
    Re: [PATCH v5 1/2] spi: dts: Add new device property to specifcy a  wait time between word transmissions Rob Herring <robh@kernel.org> - 2015-12-19 05:20 +0100
  [PATCH v5 2/2] spi: sun4i: Add support for wait time between word transmissions Marcus Weseloh <mweseloh42@gmail.com> - 2015-12-17 12:50 +0100
    Re: [PATCH v5 2/2] spi: sun4i: Add support for wait time between  word transmissions Maxime Ripard <maxime.ripard@free-electrons.com> - 2015-12-18 21:50 +0100
      Re: [PATCH v5 2/2] spi: sun4i: Add support for wait time between word transmissions Marcus Weseloh <mweseloh42@gmail.com> - 2015-12-20 13:50 +0100

csiph-web