Date: Mon, 16 Jun 2003 16:43:39 -0700 (PDT) From: Doug Ambrisko <ambrisko@ambrisko.com> To: Scott Long <scottl@freebsd.org> Cc: John-Mark Gurney <gurney_j@efn.org> Subject: Re: make /dev/pci really readable Message-ID: <200306162343.h5GNhdnl091211@www.ambrisko.com> In-Reply-To: <3EEE2B31.4020406@freebsd.org>
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Scott Long writes: | You should not always assume that reading PCI registers has no | side-effects. It is certainly legal and possible for a PCI device to | detect the read request and alter the contents of the register (or some | other register) as a side effect, or change an internal state machine. | 'Fixing' the various bits to allow unpriviledged access to 'pciconf -r' | is dangerous since you would have to teach the system about every pci | device in existance and how to trap on registers that have side-effects. I seem to recall reading some PCI chip spec. for a chip I was working on that did a reset on read of that register. I can't recall which or where so don't take this as fact but a distant memory. Doug A.
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