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    SubjectRe: [PATCH] synclink_gt fix transmit race and timeout
    On Tue, 23 Jun 2009 10:16:01 -0500 Paul Fulghum <> wrote:

    > On Mon, 2009-06-22 at 23:19 -0700, Andrew Morton wrote:
    > > On Tue, 16 Jun 2009 14:44:11 -0500 Paul Fulghum <> wrote:
    > >
    > > > Fix race condition when adding transmit data to active DMA buffer ring
    > > > that can cause transmit stall.
    > > It's not a terribly good changelog, sorry.
    > > It fails to describe the race condition?
    > I attempted to say what was done in the change log and
    > let the patch describe the details of how it was done.
    > But I can see that might not be enough.
    > How's this? :
    > If after adding transmit data to the transmit DMA ring the
    > transmit DMA controller has become inactive before reading
    > the new data and the serial transmitter is still active sending
    > data already in the transmit FIFO and/or shift register,
    > then wait for the serial transmitter to become idle before
    > reactivating the transmit DMA controller.
    > Otherwise the transmit DMA controller may present the
    > new data to the serial transmitter in a small timing window
    > just as the serial transmitter transitions to the idle state.
    > Hitting this window results in the serial transmitter entering
    > an inconsistent state where it does not process the new data
    > and does not signal the transition to the idle state.
    > >From the driver perspective, this condition appears as an
    > active transmit DMA controller (correct) with unsent DMA buffers
    > (correct) and an active serial transmitter (wrong), even though
    > no data is actually being sent. When all the DMA buffers are full,
    > no further data is accepted from a user application calling
    > write() until a timeout occurs and the transmitter and
    > DMA controller are reset.

    That covers it ;) But I stil lcan't work out whether we shoul backport
    this into -stable.

    > If this is good enough, I will resubmit the patch with
    > the updated change log.

    I updated the patch.

    I did have a couple of other comments on the patch which seem to have
    been missed?

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