linux-kernel - [PATCH 11/11] staging: gasket: Update device virtual address comment

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Date:   Sun, 14 Oct 2018 21:59:27 -0700
From:   Todd Poynor <toddpoynor@...il.com>
To:     Rob Springer <rspringer@...gle.com>,
        Ben Chan <benchan@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        Nick Ewalt <nicholasewalt@...gle.com>,
        Todd Poynor <toddpoynor@...gle.com>
Subject: [PATCH 11/11] staging: gasket: Update device virtual address comment

From: Nick Ewalt <nicholasewalt@...gle.com>

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@...gle.com>
Signed-off-by: Todd Poynor <toddpoynor@...gle.com>
---
 drivers/staging/gasket/gasket_page_table.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/gasket/gasket_page_table.c b/drivers/staging/gasket/gasket_page_table.c
index c2fbab74194f8..5b398b7ba81d3 100644
--- a/drivers/staging/gasket/gasket_page_table.c
+++ b/drivers/staging/gasket/gasket_page_table.c
@@ -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
-- 
2.19.0.605.g01d371f741-goog