block: refactor the bounce buffering code

Get rid of all the PFN arithmetics and just use an enum for the two
remaining options, and use PageHighMem for the actual bounce decision.

Add a fast path to entirely avoid the call for the common case of a queue
not using the legacy bouncing code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Link: https://lore.kernel.org/r/20210331073001.46776-8-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 8 insertions, 34 deletions

diff --git a/block/blk-settings.c b/block/blk-settings.c
index f9937dd2810e..9c009090c4b5 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -7,7 +7,6 @@
 #include <linux/init.h>
 #include <linux/bio.h>
 #include <linux/blkdev.h>
-#include <linux/memblock.h>	/* for max_pfn/max_low_pfn */
 #include <linux/gcd.h>
 #include <linux/lcm.h>
 #include <linux/jiffies.h>
@@ -17,11 +16,6 @@
 #include "blk.h"
 #include "blk-wbt.h"
 
-unsigned long blk_max_low_pfn;
-EXPORT_SYMBOL(blk_max_low_pfn);
-
-unsigned long blk_max_pfn;
-
 void blk_queue_rq_timeout(struct request_queue *q, unsigned int timeout)
 {
 	q->rq_timeout = timeout;
@@ -55,7 +49,7 @@ void blk_set_default_limits(struct queue_limits *lim)
 	lim->discard_alignment = 0;
 	lim->discard_misaligned = 0;
 	lim->logical_block_size = lim->physical_block_size = lim->io_min = 512;
-	lim->bounce_pfn = (unsigned long)(BLK_BOUNCE_ANY >> PAGE_SHIFT);
+	lim->bounce = BLK_BOUNCE_NONE;
 	lim->alignment_offset = 0;
 	lim->io_opt = 0;
 	lim->misaligned = 0;
@@ -92,28 +86,16 @@ EXPORT_SYMBOL(blk_set_stacking_limits);
 /**
  * blk_queue_bounce_limit - set bounce buffer limit for queue
  * @q: the request queue for the device
- * @max_addr: the maximum address the device can handle
+ * @bounce: bounce limit to enforce
  *
  * Description:
- *    Different hardware can have different requirements as to what pages
- *    it can do I/O directly to. A low level driver can call
- *    blk_queue_bounce_limit to have lower memory pages allocated as bounce
- *    buffers for doing I/O to pages residing above @max_addr.
+ *    Force bouncing for ISA DMA ranges or highmem.
+ *
+ *    DEPRECATED, don't use in new code.
  **/
-void blk_queue_bounce_limit(struct request_queue *q, u64 max_addr)
+void blk_queue_bounce_limit(struct request_queue *q, enum blk_bounce bounce)
 {
-	unsigned long b_pfn = max_addr >> PAGE_SHIFT;
-
-#if BITS_PER_LONG == 64
-	/*
-	 * Assume anything <= 4GB can be handled by IOMMU.  Actually
-	 * some IOMMUs can handle everything, but I don't know of a
-	 * way to test this here.
-	 */
-	q->limits.bounce_pfn = max(max_low_pfn, b_pfn);
-#else
-	q->limits.bounce_pfn = b_pfn;
-#endif
+	q->limits.bounce = bounce;
 }
 EXPORT_SYMBOL(blk_queue_bounce_limit);
 
@@ -536,7 +518,7 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
 					b->max_write_zeroes_sectors);
 	t->max_zone_append_sectors = min(t->max_zone_append_sectors,
 					b->max_zone_append_sectors);
-	t->bounce_pfn = min_not_zero(t->bounce_pfn, b->bounce_pfn);
+	t->bounce = max(t->bounce, b->bounce);
 
 	t->seg_boundary_mask = min_not_zero(t->seg_boundary_mask,
 					    b->seg_boundary_mask);
@@ -916,11 +898,3 @@ void blk_queue_set_zoned(struct gendisk *disk, enum blk_zoned_model model)
 	}
 }
 EXPORT_SYMBOL_GPL(blk_queue_set_zoned);
-
-static int __init blk_settings_init(void)
-{
-	blk_max_low_pfn = max_low_pfn - 1;
-	blk_max_pfn = max_pfn - 1;
-	return 0;
-}
-subsys_initcall(blk_settings_init);