[1/2] usbip: fix off-by-one frame number calculation

Message ID 20171107104010.2884193-1-arnd@arndb.de
State Accepted
Commit 15081e85cca45e495144eb0c108926e629fde486
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Series
  • [1/2] usbip: fix off-by-one frame number calculation
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Commit Message

Arnd Bergmann Nov. 7, 2017, 10:39 a.m.
vgadget_get_frame returns a frame number from 0 to 2046, which
may require an expensive division operation to wrap at one lower
than the usual number.

I can't see any reason for this, and all other drivers wrap at
a power-of-two number. My best explanation is that it was a simple
typo, so I'm changing the % modulo operator into a cheaper bitmask
that the other drivers use, to make it wrap after 0x7ff rather than
before it.

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

---
 drivers/usb/usbip/vudc_dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

-- 
2.9.0

Comments

Krzysztof Opasiak Nov. 7, 2017, 11:21 a.m. | #1
On 11/07/2017 11:39 AM, Arnd Bergmann wrote:
> vgadget_get_frame returns a frame number from 0 to 2046, which

> may require an expensive division operation to wrap at one lower

> than the usual number.

> 

> I can't see any reason for this, and all other drivers wrap at

> a power-of-two number. My best explanation is that it was a simple

> typo, so I'm changing the % modulo operator into a cheaper bitmask

> that the other drivers use, to make it wrap after 0x7ff rather than

> before it.

> 

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


Looks good to me:
Reviewed-by: Krzysztof Opasiak <k.opasiak@samsung.com>


-- 
Krzysztof Opasiak
Samsung R&D Institute Poland
Samsung Electronics
shuah Nov. 7, 2017, 9:10 p.m. | #2
On 11/07/2017 04:21 AM, Krzysztof Opasiak wrote:
> 

> 

> On 11/07/2017 11:39 AM, Arnd Bergmann wrote:

>> vgadget_get_frame returns a frame number from 0 to 2046, which

>> may require an expensive division operation to wrap at one lower

>> than the usual number.

>>

>> I can't see any reason for this, and all other drivers wrap at

>> a power-of-two number. My best explanation is that it was a simple

>> typo, so I'm changing the % modulo operator into a cheaper bitmask

>> that the other drivers use, to make it wrap after 0x7ff rather than

>> before it.

>>

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

> 

> Looks good to me:

> Reviewed-by: Krzysztof Opasiak <k.opasiak@samsung.com>

> 


Acked-by: Shuah Khan <shuahkh@osg.samsung.com>


thanks,
-- Shuah

Patch

diff --git a/drivers/usb/usbip/vudc_dev.c b/drivers/usb/usbip/vudc_dev.c
index 0c07348820ea..16fb4f85a6f6 100644
--- a/drivers/usb/usbip/vudc_dev.c
+++ b/drivers/usb/usbip/vudc_dev.c
@@ -145,7 +145,7 @@  static int vgadget_get_frame(struct usb_gadget *_gadget)
 	do_gettimeofday(&now);
 	return ((now.tv_sec - udc->start_time.tv_sec) * 1000 +
 			(now.tv_usec - udc->start_time.tv_usec) / 1000)
-			% 0x7FF;
+			& 0x7FF;
 }
 
 static int vgadget_set_selfpowered(struct usb_gadget *_gadget, int value)