On Tue, Feb 04, 2014 at 06:34:13PM +0000, Martyn Welch wrote: > On 04/02/14 16:34, Michael Kenney wrote: > >Hi Martyn, > > > >On Tue, Feb 4, 2014 at 7:28 AM, Martyn Welch <martyn.we...@ge.com > ><mailto:martyn.we...@ge.com>> wrote: > > > > On 28/12/13 00:34, Michael Kenney wrote: > > > > Hi Martyn, > > > > On Fri, Dec 27, 2013 at 4:23 PM, Martyn Welch > > <mar...@welchs.me.uk <mailto:mar...@welchs.me.uk>> wrote: > > > > On 27/12/13 20:15, Michael Kenney wrote: > > > > > > We are using the vme_tsi148 bridge driver along with the > > vme_user > > driver to access the VME boards. The A/D board requires > > D32 bus cycles > > and the VME master window is configured accordingly, > > however, when > > monitoring the bus cycles with a logic analyzer, we > > noticed that the > > CPU is transferring one byte at a time (i.e. four D8 > > transfers rather > > than one D32). > > > > Is this the expected behavior of the tsi148 driver? > > > > > > Hi Mike, > > > > This is certainly not the expected behaviour - if the window > > is configured > > for D32 then it should do 32 bit transfers where possible. > > > > I've heard of this happening recently, but haven't yet been > > able to > > replicate it. Which VME board are you running Linux on and > > which flavour of > > Linux? > > > > > > I'm running Debian 7.2 with kernel 3.2 on a Fastwel CPC600 > > (Pentium M > > based CPU board). > > > > > > I haven't forgotten about this, still not sure exactly what is > > happening. > > > > Is your install/kernel 32 or 64 bit? > > > > Are you doing single 32-bit transfers, or are you seeing this on > > longer transfers (i.e. copying a buffer full of data)? > > > > > >Thanks for getting back to me. > > > >I'm running a 32-bit kernel and I see this behavior on all transfers > >regardless of buffer size. > > > > Gah! Thought I could see what may be causing it in 64-bit kernels, but not > 32-bit (my x86 asm is not particularly hot). > > I think we /may/ be hitting issues with how the memcpy function gets > implemented on specific architectures. The tsi148 is a PCI/X to VME bridge, > if it receives a series of 8-bit reads or writes, it translates these to > 8-bit reads or writes on the VME bus, which is not necessarily what we want. > > According to the data sheet, the card you are using has an Intel 6300ESB > ICH, which seems to be PCI/X (so we can rule out PCIe to PCI/X bridges or > something like that doing nasty things). > > I think (if I follow everything correctly) then the memcpy for 32-bit is > handled by __memcpy in arch/x86/include/asm/string_32.h: > > static __always_inline void *__memcpy(void *to, const void *from, size_t n) > { > int d0, d1, d2; > asm volatile("rep ; movsl\n\t" > "movl %4,%%ecx\n\t" > "andl $3,%%ecx\n\t" > "jz 1f\n\t" > "rep ; movsb\n\t" > "1:" > : "=&c" (d0), "=&D" (d1), "=&S" (d2) > : "0" (n / 4), "g" (n), "1" ((long)to), "2" > ((long)from) > : "memory"); > return to; > } > > I'd expected this function to use movl (32-bit moves) where possible, but > movsb to get to naturally aligned moves (which is something that we deal > with in the VME code already to use 16-bit reads where we can). > > Greg (as co-maintainer of the VME subsystem :-) ), Am I reading this right?
Yes, but why would it matter if we copy by bytes, bits, or dwords to a memory-backed bus? By definition, that shouldn't matter. If it does matter, then we shouldn't be using memcpy, or relying on the compiler to do the copying, but rather we need to use a write() function instead as this would be IO memory that does care about this type of thing. Does that help? thanks, greg k-h _______________________________________________ devel mailing list de...@linuxdriverproject.org http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
