cppi_next_tx_segment is not checking for Transmit Buffer Descriptor
ownership before modifying parameters.
Transmit Buffer Descriptor ram is shared between the host processor and
the DMA. The "Ownership" bit is set by the host processor to give the
DMA ownership of the Transmit Buffer Descriptor, and the bit is cleared
by the DMA to return ownership to the host processor.
On USB Tx, when the system is heavily loaded, cppi_next_tx_segment can
overwrite a Transmit Buffer Descriptor that is still owned by the DMA,
causing DMA truncation error to fire, resulting in a channel abort. This
proposed fix adds a check for host processor ownership of the bd and
does not proceed to program it until the DMA has ended ownership.
Condition rarely occurs, so USB write speed is not negatively impacted.
Tested on DM365
Signed-off-by: Paul Stuart <paul_stuart@xxxxxxxxxxxx>
---
V2: Wrapped test in unlikely macro as this event _shouldn't_ occur often. Fixed formatting, per Sergei's advice.
--- a/drivers/usb/musb/cppi_dma.c 2010-12-06 20:09:04.000000000 -0800
+++ b/drivers/usb/musb/cppi_dma.c 2010-12-07 11:22:04.000000000 -0800
@@ -625,6 +625,14 @@ cppi_next_tx_segment(struct musb *musb,
* size; for RNDIS there _is_ only that last packet.
*/
for (i = 0; i < n_bds; ) {
+
+ /* wait for DMA to release ownership of this bd */
+ if (unlikely(bd->hw_options & CPPI_OWN_SET)) {
+ do {
+ cpu_relax();
+ } while (bd->hw_options & CPPI_OWN_SET);
+ }
+
if (++i < n_bds && bd->next)
bd->hw_next = bd->next->dma;
else
--
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