Re: [PATCH 1/2] spi: spi-omap2-mcspi.c: Add dts for slave deviceconfiguration.

From: Illia Smyrnov
Date: Thu Jun 06 2013 - 06:09:16 EST

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

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

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