Probs with PCI bus master DMA to user space
Hello! I think the following is general problem, but i haven't found any information about that yet.. I'm currently writing a driver which wants to transfer data between main memory and a PCI device. The data buffers are allocated by the program which uses the driver and therefore lie in the user space. Pointers to the data buffers are as usual passed to the driver with read() and write() calls. The driver then initializes a DMA transfer where the PCI device is bus master. The driver of course has to split the transfer into several smaller ones, because the memory pages which contain the data buffers could be spread across the complete memory. Before i can actually start the transfer, i have to make sure that the pages are not swapped and remain locked during the transfer. The problem I have is: Is there an efficient way to lock the pages which are accessed by the DMA? The program using the driver can't use mlock(), because the program does not know about DMA transfers somewhere below the driver. The driver should not use mlock() either, because i think that the execution of mlock() takes about as long as copying the data directly with copy_from/to_user(). Additionally, I could not unlock() the memory after the transfer, because the main program might have locked the same memory area and wants the memory to remain locked. So what can i do then? bye - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: Probs with PCI bus master DMA to user space
> Allocate the buffers in the kernel and mmap() them into user space But the buffers are usually allocated with malloc() by any application which wants to use my driver.. otherwise my driver would have to offer a malloc-like function, but I can hardly force the application to use my own malloc function. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: Probs with PCI bus master DMA to user space
Jeff Garzik wrote:
> > But the buffers are usually allocated with malloc() by any application
> > which wants to use my driver.. otherwise my driver would have to offer a
> > malloc-like function, but I can hardly force the application to use my
> > own malloc function.
>
> If you are writing the driver, sure you can.
??
The application is doing something like
fd = open("/dev/mydriver");
buf = malloc();
fill_buffer_with_data(buf);
write(fd,buf);
And now i should tell the programmer not to use malloc() but my special
driver-malloc?
Or do you mean something different?
Norbert
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Re: Probs with PCI bus master DMA to user space
Jeff Garzik wrote: > > On Tue, 20 Feb 2001, Norbert Roos wrote: > > > Jeff Garzik wrote: > > > > > > But the buffers are usually allocated with malloc() by any application > > > > which wants to use my driver.. otherwise my driver would have to offer a > > fd = open(...); > buf = mmap(fd, ...); > fill_buffer_with_data(buf); > ioctl(fd, ...); /* tell kernel data is there */ > Hm hm - this is exactly what i wanted to avoid: The application should not be modified only to be able to use my driver - and if it is using malloc(), it would have to be modified.. Thanks anyway! Norbert - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: Problem with DMA buffer (in 2.2.15)
Christoph Baumann wrote: > is to do this in steps of PAGE_SIZE. What I'm looking for is a kernel routine > to force the mapping of previous unmapped pages. Browsing through the source > in mm/ I found make_pages_present(). Could this be the solution? I hadn't the Have you already looked at mlock(2)? Norbert - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
