Date: Mon, 16 Jun 2003 16:57:52 -0700 (PDT) From: Doug Ambrisko <ambrisko@ambrisko.com> To: arch@freebsd.org Subject: Re: make /dev/pci really readable Message-ID: <200306162357.h5GNvr2O091991@www.ambrisko.com> In-Reply-To: <200306162343.h5GNhdnl091211@www.ambrisko.com>
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Doug Ambrisko writes: | 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. I meant to add this but didn't ... If the register could get cleared then the device driver could get hosed and that would be bad. This is what I was thinking about. Doug A.
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