Date: Thu, 13 Oct 2011 00:59:35 -0700 From: perryh@pluto.rain.com To: pyunyh@gmail.com Cc: fodillemlinkarim@gmail.com, freebsd-net@freebsd.org, kob6558@gmail.com Subject: Re: if_msk.c link negotiation / packet drops Message-ID: <4e969a67.YJyWMt0xI7pFL%2BxJ%perryh@pluto.rain.com> In-Reply-To: <20111012170347.GA9138@michelle.cdnetworks.com> References: <4E94637A.5090607@gmail.com> <20111011171029.GA5661@michelle.cdnetworks.com> <CAN6yY1tWQZwdqgYdN3uBBdXiGQ2OFDMYbSjhEUeTimHjBnR9iA@mail.gmail.com> <4E959F06.6040906@gmail.com> <20111012170347.GA9138@michelle.cdnetworks.com>
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YongHyeon PYUN <pyunyh@gmail.com> wrote: > On Wed, Oct 12, 2011 at 10:07:02AM -0400, Karim wrote: > > ... why are we ORing the same call twice isn't the same thing > > as calling it once: > > > > bmsr = PHY_READ(sc, E1000_SR) | PHY_READ(sc, E1000_SR); > > The E1000_SR_LINK_STATUS bit is latched low so it should be read > twice. It might not be a bad idea to check the generated code to be sure that the read _is_ being done twice. An optimizer might well come to the same conclusion as Karim, and discard the "redundant" second instance (unless there's a "volatile" declaration somewhere in the expansion of PHY_READ, to explicitly indicate that it has side effects).
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