On 06/05/2013 02:57 PM, Mark Brown wrote:
On Wed, Jun 05, 2013 at 02:39:57PM +0300, Illia Smyrnov wrote:
+SPI Controller specific data in SPI slave nodes:
+- The spi slave nodes can provide the following information which is used
+ by the spi controller:
+ - ti,spi-turbo-mode: Set turbo mode for this device.
+
What is turb mode and
According to OMAP TRM [1] MCSPI turbo mode improves the throughput of
the SPI interface when a single channel is enabled by allowing transfers
until the shift register and the MCSPI_RXx register are full.
I tested turbo mode using KS8851 SPI Ethernet controller on Blaze with
OMAP4460 and nuttcp tool with -r for RX throughput measuring. Enabling
turbo mode was increased throughput form 7.5538 Mbps to 8.3848 Mbps
why would we not want to just enable it all the
time?
Turbo mode gives the expected results not for all cases. There are some
limitations:
- works only if a single channel is enabled (no effect when several
channels are enable);
- improves the throughput on RX direction only;
- effective only when a transfer exceeds two words. For single SPI
word transfers OMAP TRM [1] recommends deactivate turbo mode.
So it is useful to have the property in DT, that allow us to switch
turbo mode off/on for certain slave.
Based on this documentation it's not really possible to tell...
I will add turbo mode description to documentation in the next patch version
[1]: http://www.ti.com/lit/ug/swpu235z/swpu235z.pdf
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