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[ Upstream commit 84fb6c7feb1494ebb7d1ec8b95cfb7ada0264465 ] It was noticed that unbinding and rebinding the KSZ8851 ethernet resulted in the driver reporting "failed to read device ID" at probe. Probing the reset line with a 'scope while repeatedly attempting to bind the driver in a shell loop revealed that the KSZ8851 RSTN pin is constantly held at zero, meaning the device is held in reset, and does not respond on the SPI bus. Experimentation with the startup delay on the regulator set to 50ms shows that the reset is positively released after 20ms. Schematics for this board are not available, and the traces are buried in the inner layers of the board which makes tracing where the RSTN pin extremely difficult. We can only guess that the RSTN pin is wired to a reset generator chip driven off the ethernet supply, which fits the observed behaviour. Include this delay in the regulator startup delay - effectively treating the reset as a "supply stable" indicator. This can not be modelled as a delay in the KSZ8851 driver since the reset generation is board specific - if the RSTN pin had been wired to a GPIO, reset could be released earlier via the already provided support in the KSZ8851 driver. This also got confirmed by Peter Ujfalusi <peter.ujfalusi@ti.com> based on Blaze schematics that should be very close to SDP4430: TPS22902YFPR is used as the regulator switch (gpio48 controlled): Convert arm boot_lock to raw The VOUT is routed to TPS3808G01DBV. (SCH Note: Threshold set at 90%. Vsense: 0.405V). According to the TPS3808 data sheet the RESET delay time when Ct is open (this is the case in the schema): MIN/TYP/MAX: 12/20/28 ms. Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk> Reviewed-by: Peter Ujfalusi <peter.ujfalusi@ti.com> [tony@atomide.com: updated with notes from schematics from Peter] Signed-off-by: Tony Lindgren <tony@atomide.com> Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.