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We observed the initial probe of the da9063 failing in da9063_get_device_type in about 30% of boots on a Xilinx ZynqMP based board. The problem originates in da9063_i2c_blockreg_read, which uses a single bus transaction to turn the register page and then read a register. On the bus, this should translate to a write to register 0, followed by a read to the target register, separated by a repeated start. However, we found that after the write to register 0, the controller sometimes continues directly with the register address of the read request, without sending the chip address or a repeated start in between, which makes the read request invalid. To fix this, separate turning the page and reading the register into two separate transactions. This brings the initialization code in line with the rest of the driver, which uses register maps (which to my knowledge do not use repeated starts after turning the page). This has been included in our kernel for several months and was recently included in a shipped product. For us, it reliably fixes the issue, and we have not observed any new issues. While the underlying problem is probably with the i2c controller or its driver, I still propose a change here in the interest of robustness: First, I'm not sure this issue can be fixed on the controller side, since there are other issues related to repeated start which can't (AR# 60695, AR# 61664). Second, similar problems might exist with other controllers. Signed-off-by: Jens Kehne <jens.kehne@agilent.com> Link: https://lore.kernel.org/r/20250804133754.3496718-1-jens.kehne@agilent.com Signed-off-by: Lee Jones <lee@kernel.org> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
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.