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There is no need for complex checking between the last consumed index
and current consumed index, a simple subtraction will do.
This also eliminates the possibility of a permanent transmit queue stall
under the following conditions:
- one CPU bursts ring->size worth of traffic (up to 256 buffers), to the
point where we run out of free descriptors, so we stop the transmit
queue at the end of bcm_sysport_xmit()
- because of our locking, we have the transmit process disable
interrupts which means we can be blocking the TX reclamation process
- when TX reclamation finally runs, we will be computing the difference
between ring->c_index (last consumed index by SW) and what the HW
reports through its register
- this register is masked with (ring->size - 1) = 0xff, which will lead
to stripping the upper bits of the index (register is 16-bits wide)
- we will be computing last_tx_cn as 0, which means there is no work to
be done, and we never wake-up the transmit queue, leaving it
permanently disabled
A practical example is e.g: ring->c_index aka last_c_index = 12, we
pushed 256 entries, HW consumer index = 268, we mask it with 0xff = 12,
so last_tx_cn == 0, nothing happens.
Fixes:
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| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| firmware | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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.