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staging: gasket: Update device virtual address comment

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Add that number of page table entries and extended address bit offset
are configurable. Update example virtual address format to be more
consistent with typical usage.

Signed-off-by: Nick Ewalt <nicholasewalt@google.com>
Signed-off-by: Todd Poynor <toddpoynor@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Nick Ewalt 2018-10-14 21:59:27 -07:00 committed by Greg Kroah-Hartman
parent df5f470de0
commit c2aed5648f
1 changed files with 11 additions and 3 deletions
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14
drivers/staging/gasket/gasket_page_table.c
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@ -10,10 +10,18 @@
*
* This file assumes 4kB pages throughout; can be factored out when necessary.
*
* Address format is as follows:
* There is a configurable number of page table entries, as well as a
* configurable bit index for the extended address flag. Both of these are
* specified in gasket_page_table_init through the page_table_config parameter.
*
* The following example assumes:
* page_table_config->total_entries = 8192
* page_table_config->extended_bit = 63
*
* Address format:
* Simple addresses - those whose containing pages are directly placed in the
* device's address translation registers - are laid out as:
* [ 63 - 40: Unused | 39 - 28: 0 | 27 - 12: page index | 11 - 0: page offset ]
* [ 63 - 25: 0 | 24 - 12: page index | 11 - 0: page offset ]
* page index: The index of the containing page in the device's address
* translation registers.
* page offset: The index of the address into the containing page.
@ -21,7 +29,7 @@
* Extended address - those whose containing pages are contained in a second-
* level page table whose address is present in the device's address translation
* registers - are laid out as:
* [ 63 - 40: Unused | 39: flag | 38 - 37: 0 | 36 - 21: dev/level 0 index |
* [ 63: flag | 62 - 34: 0 | 33 - 21: dev/level 0 index |
* 20 - 12: host/level 1 index | 11 - 0: page offset ]
* flag: Marker indicating that this is an extended address. Always 1.
* dev index: The index of the first-level page in the device's extended