From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <392EE49F.234413C5@embeddededge.com> Date: Fri, 26 May 2000 16:54:55 -0400 From: Dan Malek MIME-Version: 1.0 To: Tom Roberts CC: linuxppc-embedded@lists.linuxppc.org Subject: Re: Curious limitation in copy_from_user() References: <392EDED5.33749798@lucent.com> Content-Type: text/plain; charset=us-ascii Sender: owner-linuxppc-embedded@lists.linuxppc.org List-Id: Tom Roberts wrote: > > While porting Linux PPC to my hardware, I discovered a curious > limitation in copy_from_user() -- it cannot handle uncached memory. Yeeup. We have discussed that before. The later/newer kernels trap this fault and emulate the data move. Although there are some cases as you just discovered, the larger sample indicated access to uncached memory spaces required special handling so this wasn't going to be a problem. The only choice is to not take advantage of the performance enhancements, which didn't seem like a good thing. In your case, you will have to write your own function to validate the user buffer space and then copy the data in a loop. Perhaps we need a copy_from_user_uncached() or something. -- Dan ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/