From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <3CF51E31.6000302@embeddededge.com> Date: Wed, 29 May 2002 14:30:09 -0400 From: Dan Malek MIME-Version: 1.0 To: Neil Wilson Cc: linuxppc-embedded@lists.linuxppc.org Subject: Re: pci_consistent_alloc & mpc107 snoop References: <002101c20736$bb52f640$7c99883e@m5axc> Content-Type: text/plain; charset=us-ascii; format=flowed Sender: owner-linuxppc-embedded@lists.linuxppc.org List-Id: Neil Wilson wrote: > I hope someone can enlighten me ..... Heh :-) > Am I right in thinking that pci_consistent_alloc gets me > uncached memory ?, if not is there an easy way to modify the pages allocated > ? It's gets memory for you that is dma consistent, not necessarily uncached. It will be uncached on processors that don't have cache snooping, but it will be cached on processors that are known to snoop the bus. > Our hardware designer therefore wants the pci ethernet to use uncached > buffers & > also to have the 107 pci snoop disabled. Linux usually assumes major hardware features work :-) There are working boards with 7450/107 combinations. I don't know what your fpga may be doing that causes problems. > .... I have disabled snoop in the boot > code (ppcboot) and the ethernet card still works, but now it does not work > under Linux (it used to be fine with snoop enabled, nfs etc all worked). You need to tell Linux the processor doesn't support snooping. There is a configuration option CONFIG_NOT_COHERENT_CACHE that we use on processors that don't have cache snooping, but I don't know how well it will work in your case. I know the cache management functions are not designed to work with L2 and L3 caches, so there will be lots of work needed to keep the caches on a 74xx consistent. > Any ideas ....? I would certainly verify this "errata" is causing the trouble before making the software changes necessary to support a non-snooping 74xx processor. I'm not sure how much of an "errata" this is or simply the desire to eliminate some backward compatibility to improve bus performance. I would also find a way to measure the performance impact of such a system design, as the multiple level caches and bus snooping appear to be a significant part of the system performance. It seems weird to invest in the power of the 7450 and then cripple it by not using these features. Good luck. -- Dan ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/