Messages in this thread |  | | Date | Mon, 13 Dec 2021 15:18:11 +0100 | From | Greg Kroah-Hartman <> | Subject | Re: [PATCH 2/3] usb: mtu3: add memory barrier before set GPD's HWO |
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On Thu, Dec 09, 2021 at 11:14:23AM +0800, Chunfeng Yun wrote: > There is a seldom issue that the controller access invalid address > and trigger devapc or emimpu violation. That is due to memory access > is out of order and cause gpd data is not correct. > Make sure GPD is fully written before giving it to HW by setting its > HWO. > > Fixes: 48e0d3735aa5 ("usb: mtu3: supports new QMU format") > Cc: stable@vger.kernel.org > Reported-by: Eddie Hung <eddie.hung@mediatek.com> > Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com> > --- > drivers/usb/mtu3/mtu3_qmu.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/drivers/usb/mtu3/mtu3_qmu.c b/drivers/usb/mtu3/mtu3_qmu.c > index 3f414f91b589..34bb5ac67efe 100644 > --- a/drivers/usb/mtu3/mtu3_qmu.c > +++ b/drivers/usb/mtu3/mtu3_qmu.c > @@ -273,6 +273,8 @@ static int mtu3_prepare_tx_gpd(struct mtu3_ep *mep, struct mtu3_request *mreq) > gpd->dw3_info |= cpu_to_le32(GPD_EXT_FLAG_ZLP); > } > > + /* make sure GPD is fully written before giving it to HW */ > + mb();
So this means you are using mmio for this structure? If so, shouldn't you be using normal io memory read/write calls as well and not just "raw" pointers like this:
> gpd->dw0_info |= cpu_to_le32(GPD_FLAGS_IOC | GPD_FLAGS_HWO);
Are you sure this is ok?
Sprinkling around mb() calls is almost never the correct solution.
If you need to ensure that a write succeeds, shouldn't you do a read from it afterward? Many busses require this, doesn't yours?
> > mreq->gpd = gpd; > @@ -306,6 +308,8 @@ static int mtu3_prepare_rx_gpd(struct mtu3_ep *mep, struct mtu3_request *mreq) > gpd->next_gpd = cpu_to_le32(lower_32_bits(enq_dma)); > ext_addr |= GPD_EXT_NGP(mtu, upper_32_bits(enq_dma)); > gpd->dw3_info = cpu_to_le32(ext_addr); > + /* make sure GPD is fully written before giving it to HW */ > + mb();
Again, mb(); does not ensure that memory-mapped i/o actually hits the HW. Or if it does on your platform, how?
mb() is a compiler barrier, not a memory write to a bus barrier. Please read Documentation/memory-barriers.txt for more details.
thanks,
greg k-h
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