Am Samstag, 13. September 2008 20:33 meinte Matthew Wilcox: > On Sat, Sep 13, 2008 at 12:15:34PM -0600, Grant Grundler wrote: > > On Fri, Sep 12, 2008 at 11:29:39PM +0200, Felix Frey wrote: > > > Dear readers > > > > > > I have a problem with a linux PCI driver I've written. The driver > > > supports a kind of a data acquisition system, which is implemented in a > > > programable logic device. It's pci interface does not have master > > > capability, so every data exchange is initiated by the CPU. > > > > > > Well, the driver is fairly simple and simply handles data exchange. It > > > has to transfer chunks of data from and to the device. To make it fast > > > I'd like to use burst transfers, which are supported by the device. > > > Within the driver I use the kernel functions memcpy_fromio and > > > memcpy_toio to initiate a transfer. > > > This works so far, however, there are no burst transfers. The bridge > > > does a complete address cycle for every single word which is a big > > > waste of time. > > > > In order to get multiple data cycles per address cycle, either the CPU > > and/or the chipset needs to be told it's ok to coalesce the write > > transactions (memcpy_toio). OK. What's the way to go? Does it mean to fiddle around with register programming of the bridge or are there any architecture independant routines in the kernels pci subsystem? > > Isn't that simply a case of marking the BAR as prefetchable? > > Memory locations are characterized as either prefetchable or > non-prefetchable. Prefetchable memory has the following characteristics: > - There are no side effects of a read operation. The read operation > cannot be destructive to either the data or any other state > information. For example, a FIFO that advances to the next data when read > would not be prefetchable. Similarly, a location that cleared a status bit > when read would not be prefetchable. > - When read, the device is required to return all bytes regardless of the > byte enables (four or eight depending upon the width of the data > transfer (refer to Section 3.8.1.)). > - Bridges are permitted to merge writes into this range (refer to > Section 3.2.6.). Unfortunately it isn't that simple. Marking the BAR's as prefetchable or not didn't do any difference. (Although it makes sense to me :-| ) Felix -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
