mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/
synced 2026-10-16 22:39:48 +00:00
No description
- C 96.9%
- Assembly 0.9%
- Rust 0.6%
- Shell 0.6%
- Python 0.5%
- Other 0.3%
b7a82103f7Due to the controller limitation to keep the chip select low during the bus idle time between the transfer, a dummy cs workaround was used when this driver was first upstreamed to the kernel. It basically picks the dummy cs as !actual_cs so typically dummy cs is 1 when most of the case only cs 0 is used in the board design. Then invert the polarity of both cs and tell the controller to start the transfers using dummy cs. Assuming both cs are active low before the inversion, effectively this keeps dummy cs high and actual cs low during the transfer and workaround the issue. This workaround implies that dummy cs 1 pin has to be set to chip selection function in the pinmux when the transfer clock is above 25MHz. The old chips likely have default pinmux set to chip select on the dummy cs pin so it works but this is not case for the new Broadband BCA chips and this workaround stop working. This is specifically an issue to support SPI NAND and SPI NOR flash because these flash devices can typically run at or above 100MHz. This patch utilizes the prepend feature of the controller to combine the multiple transfers in the same message to a single transfer when possible. This way there is no need to keep clock low between transfers and solve the issue without any hardware requirement. Multiple transfers within a SPI message may be combined into one transfer if the following are all true: * One or more half duplex write transfer in single bit mode * Optional full duplex read/write at the end * No delay and cs_change between transfers Most of the SPI device meets this requirements such as SPI NOR, SPI NAND flash, Broadcom SPI voice card and etc. For any SPI message that does not meet the above requirement to combine the transfers, we switch to original dummy cs mode but limit the clock rate to the safe 25MHz. This is the default auto transfer mode and it makes sure all the SPI message can be supported automatically under the hood. This patch also adds the driver sysfs node xfer_mode to provide the option for overriding the default auto mode and force it to dummy cs or prepend mode. Signed-off-by: William Zhang <william.zhang@broadcom.com> Link: https://lore.kernel.org/r/20230209200246.141520-12-william.zhang@broadcom.com Signed-off-by: Mark Brown <broonie@kernel.org> |
History
|
|
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| 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 Restructured Text 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.