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There is just one version of Cr50 firmware for all boards that it's used on. However, on some boards the AP communicates to the TPM via a SPI interface (i.e. Kevin) and on others, the AP communicates via an I2C interface (i.e. Reef). In order to dynamically discover which interface to configure, there are strapping resistors added to the board which enables the Cr50 to detect which configuration to implement. This CL is a first pass and is only looking at DIOA1 which is pulled high for SPI and pulled low for I2C configurations. The strapping resistor should be read when the AP is in reset prior to it attempting to drive any of the lines used for strapping. To ensure this condition is met, Cr50 will only check the strapping options following a POR (power on reset). Once the configuration type is discovered, a 'long_life' register is used to hold the result so that the result can always be available. The long_life register contents remain unchanged until a subsequent power down event. BRANCH=none BUG=chrome-os-partner:50728 TEST=manual Tested on Kevin and Reef. Verfifed by reading the stored value that the SPI configuraiton is detected for Kevin and the I2C interface is detected on Reef. In addition, verified on Kevin that the Cr50 FW version is correctly reported to the AP which means that TPM register reads via the slave SPI are functioning. Change-Id: Ibd7624ad8e3b4126f6346dce0bc72f62a3cc6d18 Signed-off-by: Scott <scollyer@chromium.org> Reviewed-on: https://chromium-review.googlesource.com/363014 Commit-Ready: Scott Collyer <scollyer@chromium.org> Tested-by: Scott Collyer <scollyer@chromium.org> Reviewed-by: Bill Richardson <wfrichar@chromium.org>