At Wed, 7 Aug 2013 13:38:20 -0400 (EDT), Alan Stern wrote: > > On Wed, 7 Aug 2013, Takashi Iwai wrote: > > > [Cc'ed to linux-usb ML] > > > > At Wed, 7 Aug 2013 16:51:49 +0200, > > Torsten Schenk wrote: > > > > > > Patch fixes URB transfer buffer allocation for midi output to be DMA-able. > > > > Is this really needed? > > That is, can't a transfer buffer be at middle of kmalloc'ed space, but > > must be always the head of the kmalloc'ed space? > > A buffer _can_ be in the middle of a kmalloc'ed space, but the CPU must > not access any of the fields around it that might occupy the same cache > line while the buffer is being used for DMA. In general, it's safest > not to put any other data in the same kmalloc'ed region with a DMA > buffer. Hrm, but does the kmalloc buffer always guarantee such cache line exclusiveness...? I thought a simple one like SLOB doesn't care. > > > @@ -32,7 +28,7 @@ > > > struct snd_rawmidi_substream *out; > > > struct urb out_urb; > > > u8 out_serial; /* serial number of out packet */ > > > - u8 out_buffer[MIDI_BUFSIZE]; > > > + u8 *out_buffer; > > > int buffer_offset; > > In this case, the CPU would access out_urb while out_buffer was in use. OK, then we need to fix sound/usb/6fire/pcm.c, too. Torsten, care to respin the patch? thanks, Takashi -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
