* Alan Stern <[EMAIL PROTECTED]> [070328 17:09]:
> On Wed, 28 Mar 2007, Tony Lindgren wrote:
>
> > OK, attached is take #3 with ifndef CONFIG_HIGHMEM. Anybody have other
> > limitations in mind?
>
> > + /*
> > + * Some systems need both transfer_buffer and transfer_dma
> > + * to revert to PIO if DMA is temporarily unavailable.
> > + * Note that transfer_buffer may not be accessible on some
> > + * systems. In that case there is no need to use it either.
> > + */
>
> It would be nice if this comment were more grammatical. Consider this
> instead:
>
> /*
> * Some systems can revert to PIO if DMA is temporarily
> * unavailable; for their sake both transfer_buffer and
> * transfer_dma must be set properly. However this is
> * possible only on systems with no high memory, since
> * DMA buffers located in high memory are not directly
> * addressable by the kernel for PIO. When high memory
> * is available, we NULL out transfer_buffer to avoid
> * keeping a stale pointer and to help spot possible
> * addressing bugs.
> */
OK, updated comments. Also updated the patch commit text.
> > if (dma) {
> > - /* hc may use _only_ transfer_dma */
> > io->urbs [i]->transfer_dma = sg_dma_address (sg + i);
> > len = sg_dma_len (sg + i);
> > - } else {
> > - /* hc may use _only_ transfer_buffer */
> > +#ifndef CONFIG_HIGHMEM
> > io->urbs [i]->transfer_buffer =
> > page_address (sg [i].page) + sg [i].offset;
>
> Insert here:
>
> +#else
> + io->urbs[i]->transfer_buffer = NULL;
>
> > +#endif
> > + } else {
> > len = sg [i].length;
> > + io->urbs [i]->transfer_buffer =
> > + page_address (sg [i].page) + sg [i].offset;
> > }
>
> Don't duplicate the old non-approved spacing style in new code. This
> should say
>
> + io->urbs[i]->transfer_buffer =
> + page_address(sg[i].page) + sg[i].offset;
>
> If you like, you can change the other occurrence of this to match.
OK, changed. New patch attached.
Regards,
Tony
From: Tony Lindgren <[EMAIL PROTECTED]>
Subject: USB: Allow transfer_buffer with transfer_dma
In case a DMA channel for an endpoint is temporarily
unavailable, the host controller driver may still be
able to transfer the data using PIO. Without this patch
the transfer_buffer is not mapped, and host controller
does not know what to use for PIO.
Signed-off-by: Tony Lindgren <[EMAIL PROTECTED]>
===================================================================
--- a/drivers/usb/core/message.c
+++ b/drivers/usb/core/message.c
@@ -412,15 +412,28 @@ int usb_sg_init (
io->urbs [i]->status = -EINPROGRESS;
io->urbs [i]->actual_length = 0;
+ /*
+ * Some systems can revert to PIO if DMA is temporarily
+ * unavailable; for their sake both transfer_buffer and
+ * transfer_dma must be set properly. However this is
+ * possible only on systems with no high memory, since
+ * DMA buffers located in high memory are not directly
+ * addressable by the kernel for PIO. When high memory
+ * is available, we NULL out transfer_buffer to avoid
+ * keeping a stale pointer and to help spot possible
+ * addressing bugs.
+ */
if (dma) {
- /* hc may use _only_ transfer_dma */
- io->urbs [i]->transfer_dma = sg_dma_address (sg + i);
- len = sg_dma_len (sg + i);
+ io->urbs[i]->transfer_dma = sg_dma_address(sg + i);
+ len = sg_dma_len(sg + i);
+#ifndef CONFIG_HIGHMEM
+ io->urbs[i]->transfer_buffer =
+ page_address(sg[i].page) + sg[i].offset;
+#endif
} else {
- /* hc may use _only_ transfer_buffer */
- io->urbs [i]->transfer_buffer =
- page_address (sg [i].page) + sg [i].offset;
- len = sg [i].length;
+ len = sg[i].length;
+ io->urbs[i]->transfer_buffer =
+ page_address(sg[i].page) + sg[i].offset;
}
if (length) {
-------------------------------------------------------------------------
Take Surveys. Earn Cash. Influence the Future of IT
Join SourceForge.net's Techsay panel and you'll get the chance to share your
opinions on IT & business topics through brief surveys-and earn cash
http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV
_______________________________________________
linux-usb-devel@lists.sourceforge.net
To unsubscribe, use the last form field at:
https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
