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Modern platforms can install more than 4GB memory, so DMA address can
larger than 32 bits. If a platform doesn't enable IOMMU, kernel needs extra
works of swiotlb to help DMA that packets reside on memory over 4GB.
The DMA addressing capability of Realtek WiFi chips is 36 bits, so set
LSB 4 bits of high 32-bit address to register and TX/RX descriptor, which
below figure shows 3-level pointers in TX direction, and RX direction is
similar but 2-level pointers only.
+--------+
| | register to head of TX BD
+---|----+
| +---------+
+-----> | TX BD | (in memory)
+----|----+
| +---------+
+------> | TX WD | (in memory)
+----|----+
| +--------+
+------> | skb |
+--------+
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://msgid.link/20240611021901.26394-1-pkshih@realtek.com
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.