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    SubjectRE: [RFC][PATCH 06/10] fec: fix uninitialized rx buffer usage
    Date
    From
    Sascha,

    > -----Original Message-----
    > From: Sascha Hauer [mailto:s.hauer@pengutronix.de]
    > Sent: Friday, December 04, 2009 5:14 AM
    > To: Amit Kucheria
    > Cc: List Linux Kernel; Herring Robert-RA7055; David S.
    > Miller; netdev@vger.kernel.org;
    > linux-arm-kernel@lists.infradead.org;
    > valentin.longchamp@epfl.ch; daniel@caiaq.de;
    > grant.likely@secretlab.ca; Nguyen Dinh-R00091
    > Subject: Re: [RFC][PATCH 06/10] fec: fix uninitialized rx buffer usage
    >
    > On Fri, Dec 04, 2009 at 04:47:06AM +0200, Amit Kucheria wrote:
    > > From: Rob Herring <r.herring@freescale.com>
    > >
    > > The fec driver was enabling receive buffer descriptor
    > without allocating
    > > the buffers. Make sure the buffer descriptors are initialized to not
    > > start receiving packets.
    > >
    > > Signed-off-by: Rob Herring <r.herring@freescale.com>
    > > Signed-off-by: Amit Kucheria <amit.kucheria@canonical.com>
    > > Cc: David S. Miller <davem@davemloft.net>
    > > Cc: netdev@vger.kernel.org
    > > ---
    > > drivers/net/fec.c | 57
    > +++++++++++++++++++++++++++--------------------------
    > > 1 files changed, 29 insertions(+), 28 deletions(-)
    > >
    > > diff --git a/drivers/net/fec.c b/drivers/net/fec.c
    > > index 16a1d58..9a8743d 100644
    > > --- a/drivers/net/fec.c
    > > +++ b/drivers/net/fec.c
    > > @@ -1658,6 +1658,7 @@ static int fec_enet_init(struct
    > net_device *dev, int index)
    > > {
    > > struct fec_enet_private *fep = netdev_priv(dev);
    > > struct bufdesc *cbd_base;
    > > + struct bufdesc *bdp;
    > > int i;
    > >
    > > /* Allocate memory for buffer descriptors. */
    > > @@ -1710,6 +1711,34 @@ static int fec_enet_init(struct
    > net_device *dev, int index)
    > > /* Set MII speed to 2.5 MHz */
    > > fep->phy_speed = ((((clk_get_rate(fep->clk) / 2 + 4999999)
    > > / 2500000) / 2) & 0x3F) << 1;
    > > +
    > > + /* Initialize the receive buffer descriptors. */
    > > + bdp = fep->rx_bd_base;
    > > + for (i = 0; i < RX_RING_SIZE; i++) {
    > > +
    > > + /* Initialize the BD for every fragment in the page. */
    > > + bdp->cbd_sc = 0;
    > > + bdp++;
    > > + }
    > > +
    > > + /* Set the last buffer to wrap */
    > > + bdp--;
    > > + bdp->cbd_sc |= BD_SC_WRAP;
    > > +
    > > + /* ...and the same for transmit */
    > > + bdp = fep->tx_bd_base;
    > > + for (i = 0; i < TX_RING_SIZE; i++) {
    > > +
    > > + /* Initialize the BD for every fragment in the page. */
    > > + bdp->cbd_sc = 0;
    > > + bdp->cbd_bufaddr = 0;
    > > + bdp++;
    > > + }
    > > +
    > > + /* Set the last buffer to wrap */
    > > + bdp--;
    > > + bdp->cbd_sc |= BD_SC_WRAP;
    > > +
    > > fec_restart(dev, 0);
    >
    > I do not really understand why this patch is needed. You move
    > the buffer
    > initialisation from fec_restart to fec_enet_init, but fec_restart is
    > called directly after the initialisation, so this shouldn't
    > change much.
    >
    > I don't need this patch on my boards, so I wonder what is really going
    > wrong here.

    It is because open also calls fec_restart after the rx buffers are
    allocated. With the code in fec_restart, it zeroes out the buffer
    descriptors that have just been setup. I can't explain how it would work
    for you.

    Regards,
    Rob

    >
    > Sascha
    >
    >
    > >
    > > /* Queue up command to detect the PHY and initialize the
    > > @@ -1730,7 +1759,6 @@ static void
    > > fec_restart(struct net_device *dev, int duplex)
    > > {
    > > struct fec_enet_private *fep = netdev_priv(dev);
    > > - struct bufdesc *bdp;
    > > int i;
    > >
    > > /* Whack a reset. We should wait for this. */
    > > @@ -1768,33 +1796,6 @@ fec_restart(struct net_device *dev,
    > int duplex)
    > > }
    > > }
    > >
    > > - /* Initialize the receive buffer descriptors. */
    > > - bdp = fep->rx_bd_base;
    > > - for (i = 0; i < RX_RING_SIZE; i++) {
    > > -
    > > - /* Initialize the BD for every fragment in the page. */
    > > - bdp->cbd_sc = BD_ENET_RX_EMPTY;
    > > - bdp++;
    > > - }
    > > -
    > > - /* Set the last buffer to wrap */
    > > - bdp--;
    > > - bdp->cbd_sc |= BD_SC_WRAP;
    > > -
    > > - /* ...and the same for transmit */
    > > - bdp = fep->tx_bd_base;
    > > - for (i = 0; i < TX_RING_SIZE; i++) {
    > > -
    > > - /* Initialize the BD for every fragment in the page. */
    > > - bdp->cbd_sc = 0;
    > > - bdp->cbd_bufaddr = 0;
    > > - bdp++;
    > > - }
    > > -
    > > - /* Set the last buffer to wrap */
    > > - bdp--;
    > > - bdp->cbd_sc |= BD_SC_WRAP;
    > > -
    > > /* Enable MII mode */
    > > if (duplex) {
    > > /* MII enable / FD enable */
    > > --
    > > 1.6.3.3
    > >
    > >
    >
    > --
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