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由 Alexander Sverdlin 提交于
I2C controller used in Keystone SoC has an undocumented peculiarity which results in SDA-SCL margins being dependent on module clock. Driving high capacity bus near its limits can result in STOP condition sometimes being understood as REPEATED-START by slaves (or NACK instead of ACK, etc...). Driving the module with higher clocks increases the margin between SDA and SCL transitions, making the operations with higher bus rates more robust. Therefore, target the module clock to 12MHz instead of 7MHz, still staying within the specification limits. Before the change STOP timing looked like this on 400kHz: SDA ----------+ +---- \ / \ / +----+ (1) SCL --+ +------------ \ / \ / +----+ (2) While only point (1) signals STOP, point (2) could be incorrectly recognized as repeated-START (almost no margin between SDA and SCL transitions). After the change there is at least 600ns margin measured between SCL fall and SDA fall during STOP generation: SDA ------+ +---- \ / \ / +----+ SCL --+ +-------- \ / \ / +----+ ->| |<- 600ns ->| |<- tSUSTO So called tSUSTO (setup time for STOP condition) is still slightly higher than 600ns, so no problem here. Signed-off-by: NAlexander Sverdlin <alexander.sverdlin@nokia.com> Acked-by: NSantosh Shilimkar <ssantosh@kernel.org> Signed-off-by: NWolfram Sang <wsa@the-dreams.de>
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