From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm@xmission.com (Eric W. Biederman) Date: Thu, 05 Aug 2004 02:14:55 +0000 Subject: Re: [Fastboot] Re: [BROKEN PATCH] kexec for ia64 Message-Id: List-Id: References: <200407261524.40804.jbarnes@engr.sgi.com> <200407261536.05133.jbarnes@engr.sgi.com> <20040730155504.2a51b1fa.rddunlap@osdl.org> <20040804233335.GD548@cup.hp.com> In-Reply-To: <20040804233335.GD548@cup.hp.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Grant Grundler Cc: "Randy.Dunlap" , linux-ia64@vger.kernel.org, Jesse Barnes , linux-kernel@vger.kernel.org, fastboot@osdl.org Grant Grundler writes: > On Wed, Aug 04, 2004 at 07:07:04AM -0600, Eric W. Biederman wrote: > > Initially that patch > > was targeted for a kernel without device_shutdown(), so I was > > likely considering the old trick of running through all of the PCI > > devices and disabling their bus master bit. > > Blindly disabling all PCI bus master bits will also kill VGA/serial > console and any USB keyboard attached to the system. VGA/serial console devices rarely need to do be bus masters so they should be fine. > I'll comment more on the "DMA is a Red Herring" when I can read > more what it is about. Most of those cases don't matter as the driver should always be calling pci_set_master() on startup. Disabling all the bus master bits on ioxapics in pci space would likely cripple the system. As they are architectural hardware and rarely have pci drivers that can enable them. In the general case it appears to be overkill, incorrect and insufficient to disable bus mastering on all PCI devices. Which is why device_shutdown() calls device specific code. Eric