Am Donnerstag, den 23.03.2017, 16:39 +0800 schrieb pierre Kuo:
Hi,
> for sitd_link and itd_link, put wmb after the last memory access to make
> sure ehci->period[frame] is visible by host before scheduling the
> descriptors
Please explain what the problem you are trying to fix is.
> Signed-off-by: pierre Kuo <vichy....@gmail.com>
> ---
> drivers/usb/host/ehci-sched.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/usb/host/ehci-sched.c b/drivers/usb/host/ehci-sched.c
> index 980a6b3..11b517c 100644
> --- a/drivers/usb/host/ehci-sched.c
> +++ b/drivers/usb/host/ehci-sched.c
> @@ -1754,8 +1754,9 @@ static void reserve_release_iso_bandwidth(struct
> ehci_hcd *ehci,
> itd->hw_next = *hw_p;
> prev->itd = itd;
> itd->frame = frame;
> - wmb();
This looks very wrong. You need to make sure that a data structure
is written to RAM before you announce it to the hardware.
The code before the wmb() initializes a structure and the write
after it announces it to the hardware. This wmb() is exactly where
it needs to be.
> *hw_p = cpu_to_hc32(ehci, itd->itd_dma | Q_TYPE_ITD);
> + /* make sure host see periodic frame change before scheduling */
> + wmb();
If you need to flush something, wmb() is the wrong primitive.
It merely ensures ordering. It is not guaranteed to flush writes
to RAM.
Regards
Oliver
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