Re: [PATCH] USB: Always map transfer_buffer (Fixes some musb_hdrc issues)
Tony Lindgren <[email protected]>
| Newsgroups | gmane.linux.usb.devel |
|---|---|
| Message-ID | <[email protected]> |
* Alan Stern <[email protected]> [070328 12:10]: > On Wed, 28 Mar 2007, Tony Lindgren wrote: > > > Hi, > > > > Here's a little patch to make sure tranfer_buffer is always if DMA > > is temporarily unavailable. I ran into this with tusb6010 that > > currently can only do limited DMA. This fixes a problem of connecting > > storage devices and doing mixed DMA/PIO access. > > Your patch isn't correct, or at least, it is very misleading. It calls > page_address() in a situation where it cannot be certain that the page > frame lies in accessible kernel memory. On some systems the value it > calculates will be garbage. > > At a minimum you need to add a comment explaining that if the page isn't > accessible, the transfer_buffer value won't ever be used. Yeah it's a bit ugly. I don't think there's currently an easy way to optimize out mapping of transfer_buffer on such systems. Here's a version with better comments. Tony ------------------------------------------------------------------------- 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 _______________________________________________ [email protected] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
usb-core-always-map-transfer-buffer.patch
(text/x-diff, 1.5 KB)
From: Tony Lindgren <[email protected]> Subject: USB: Always map transfer_buffer 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]> Index: linux-omap-2.6/drivers/usb/core/message.c =================================================================== --- linux-omap-2.6.orig/drivers/usb/core/message.c 2007-03-28 10:59:21.000000000 -0400 +++ linux-omap-2.6/drivers/usb/core/message.c 2007-03-28 14:35:00.000000000 -0400 @@ -412,16 +412,19 @@ int usb_sg_init ( io->urbs [i]->status = -EINPROGRESS; io->urbs [i]->actual_length = 0; + /* + * 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. + */ + io->urbs [i]->transfer_buffer = + page_address (sg [i].page) + sg [i].offset; 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 */ - io->urbs [i]->transfer_buffer = - page_address (sg [i].page) + sg [i].offset; + } else len = sg [i].length; - } if (length) { len = min_t (unsigned, len, length);