lkml.org 
[lkml]   [2002]   [Apr]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Date
Subjectunnecessary use of set_bit
The ohci_hub_status_data() procedure in drivers/usb/host/ohci-hub.c in
2.5.11 is broken in a couple of ways: it uses set_bit on a char *
address and it assumes little-endian byte order in the bitmap.

Here is a patch to fix both problems. As a bonus, the file ends up
one line shorter. :)

Please, people, don't use set_bit when you don't need an atomic
operation. set_bit(&x, n) is slower than x |= 1 << n on a lot of
platforms, including SMP x86 I believe. (If the bitmap is more than
one word you can use __set_bit if you don't require atomicity.)
Paul.

diff -urN linux-2.5/drivers/usb/host/ohci-hub.c pmac-2.5/drivers/usb/host/ohci-hub.c
--- linux-2.5/drivers/usb/host/ohci-hub.c Sat Apr 27 20:51:31 2002
+++ pmac-2.5/drivers/usb/host/ohci-hub.c Sat Apr 27 15:03:06 2002
@@ -67,7 +67,7 @@
ohci_hub_status_data (struct usb_hcd *hcd, char *buf)
{
struct ohci_hcd *ohci = hcd_to_ohci (hcd);
- int ports, i, changed = 0, length = 1;
+ int ports, i, mask = 0, length = 1;

ports = roothub_a (ohci) & RH_A_NDP;
if (ports > MAX_ROOT_PORTS) {
@@ -80,13 +80,7 @@

/* init status */
if (roothub_status (ohci) & (RH_HS_LPSC | RH_HS_OCIC))
- buf [0] = changed = 1;
- else
- buf [0] = 0;
- if (ports > 7) {
- buf [1] = 0;
- length++;
- }
+ mask = 1;

/* look at each port */
for (i = 0; i < ports; i++) {
@@ -94,12 +88,17 @@

status &= RH_PS_CSC | RH_PS_PESC | RH_PS_PSSC
| RH_PS_OCIC | RH_PS_PRSC;
- if (status) {
- changed = 1;
- set_bit (i + 1, buf);
- }
+ if (status)
+ mask |= 1 << (i + 1);
+ }
+ if (!mask)
+ return 0;
+ buf[0] = mask;
+ if (ports > 7) {
+ length++;
+ buf[1] = mask >> 8;
}
- return changed ? length : 0;
+ return length;
}

/*-------------------------------------------------------------------------*/
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
\
 
 \ /
  Last update: 2005-03-22 13:25    [W:0.058 / U:0.036 seconds]
©2003-2014 Jasper Spaans. Advertise on this site