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During the v6.14-rc cycles, there has been an issue with syscons which prevented TI chipid controller to probe, itself preventing the only DMA engine on AM62A with the memcpy capability to probe, which is needed for the SPI controller to work in its most efficient configuration. The SPI controller on AM62A can be used in DAC and INDAC mode, which are some kind of direct mapping vs. CPU-controlled SPI operations, respectively. However, because of hardware constraints (some kind of request line not being driven), INDAC mode cannot leverage DMA without risking to underflow the SPI FIFO. This mode costs a lot of CPU cycles. On the other side however, DAC mode can be used with and without DMA support, but in practice, DMA transfers are way more efficient because of the burst capabilities that the CPU does not have. As a result, in terms of read throughput, using a Winbond chip in 1-8-8 SDR mode, we get: - 3.5MiB/s in DAC mode without DMA - 9.0MiB/s in INDAC mode (CPU more busy) - a fluctuating 9 to 12MiB/s in DAC mode with DMA (a constant 14.5MiB/s without CPUfreq) The reason for the patch that is being reverted is that because of the syscon issue, we were using a very un-efficient DAC configuration (no DMA), but since: commit |
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| kernel | ||
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| COPYING | ||
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| README | ||
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.