Date: Sun, 01 Feb 2009 12:57:12 -0700 (MST) From: "M. Warner Losh" <imp@bsdimp.com> To: thompsa@freebsd.org Cc: freebsd-usb@freebsd.org Subject: Re: USB2 patches Message-ID: <20090201.125712.-1002120178.imp@bsdimp.com> In-Reply-To: <20090201191851.GE32503@citylink.fud.org.nz> References: <20090201190820.GB32503@citylink.fud.org.nz> <200902012014.32190.hselasky@c2i.net> <20090201191851.GE32503@citylink.fud.org.nz>
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In message: <20090201191851.GE32503@citylink.fud.org.nz>
Andrew Thompson <thompsa@freebsd.org> writes:
: > > xxx_set_channel()
: > > {
: > > ieee80211_channel c = wlan->curchan;
: > >
: > > hw_reg = array1[c];
: > > write USB register;
: > > hw_reg = array2[c];
: > > write USB register;
: > > }
: >
: > And don't forget "volatile" ...
:
: I dont understand this. c is a pointer to a valid net80211 channel which
: will never disappear.
"volatile" would be a bug here. There's no reason to use it at all,
since wlan->curchan doesn't match what ANSI-C says a volatile is for.
In addition, since it is only loaded once, there wouldn't be a need
for it even if it did meet the definition.
You *CANNOT* rely on 'volatile' fixing locking issues.
Warner
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