[v2] null_blk: use sector_div instead of do_div

Message ID 11387794.RmibjdD6Rx@wuerfel
State New
Headers show

Commit Message

Arnd Bergmann Jan. 13, 2016, 10:04 p.m.
Dividing a sector_t number should be done using sector_div rather than do_div
to optimize the 32-bit sector_t case, and with the latest do_div optimizations,
we now get a compile-time warning for this:

arch/arm/include/asm/div64.h:32:95: note: expected 'uint64_t * {aka long long unsigned int *}' but argument is of type 'sector_t * {aka long unsigned int *}'
drivers/block/null_blk.c:521:81: warning: comparison of distinct pointer types lacks a cast

This changes the newly added code to use sector_div. It is a simplified version
of the original patch, as Linus Torvalds pointed out that we should not be using
an expensive division function in the first place.

This version was suggested by Matias Bjorling.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Cc: Matias Bjorling <m@bjorling.me>
Fixes: b2b7e00148a2 ("null_blk: register as a LightNVM device")
---
[resent to Jens' correct address, sorry about the duplicates]

Comments

Jens Axboe Jan. 13, 2016, 10:11 p.m. | #1
On 01/13/2016 03:04 PM, Arnd Bergmann wrote:
> Dividing a sector_t number should be done using sector_div rather than do_div

> to optimize the 32-bit sector_t case, and with the latest do_div optimizations,

> we now get a compile-time warning for this:

>

> arch/arm/include/asm/div64.h:32:95: note: expected 'uint64_t * {aka long long unsigned int *}' but argument is of type 'sector_t * {aka long unsigned int *}'

> drivers/block/null_blk.c:521:81: warning: comparison of distinct pointer types lacks a cast

>

> This changes the newly added code to use sector_div. It is a simplified version

> of the original patch, as Linus Torvalds pointed out that we should not be using

> an expensive division function in the first place.

>

> This version was suggested by Matias Bjorling.

>

> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

> Cc: Matias Bjorling <m@bjorling.me>

> Fixes: b2b7e00148a2 ("null_blk: register as a LightNVM device")

> ---

> [resent to Jens' correct address, sorry about the duplicates]


Thanks Arnd, added.

-- 
Jens Axboe

Patch

diff --git a/drivers/block/null_blk.c b/drivers/block/null_blk.c
index 95dff91135ad..6f9587156569 100644
--- a/drivers/block/null_blk.c
+++ b/drivers/block/null_blk.c
@@ -495,17 +495,17 @@  static int null_lnvm_id(struct nvm_dev *dev, struct nvm_id *id)
 	id->ppaf.ch_offset = 56;
 	id->ppaf.ch_len = 8;
 
-	do_div(size, bs); /* convert size to pages */
-	do_div(size, 256); /* concert size to pgs pr blk */
+	sector_div(size, bs); /* convert size to pages */
+	size >>= 8; /* concert size to pgs pr blk */
 	grp = &id->groups[0];
 	grp->mtype = 0;
 	grp->fmtype = 0;
 	grp->num_ch = 1;
 	grp->num_pg = 256;
 	blksize = size;
-	do_div(size, (1 << 16));
+	size >>= 16;
 	grp->num_lun = size + 1;
-	do_div(blksize, grp->num_lun);
+	sector_div(blksize, grp->num_lun);
 	grp->num_blk = blksize;
 	grp->num_pln = 1;