[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH 1/2] Ignore RX tail kicks when RX disabled.
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH 1/2] Ignore RX tail kicks when RX disabled. |
Date: |
Thu, 18 Oct 2012 10:09:09 +0200 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Wed, Oct 17, 2012 at 08:31:46PM +0200, Dmitry Fleytman wrote:
> Device RX initization from driver's side consists of following steps:
> 1. Initialize head and tail of RX ring to 0
> 2. Enable Rx (set bit in RCTL register)
> 3. Allocate buffers, fill descriptors
> 4. Write ring tail
>
> Forth operation signals hardware that RX buffers available
> and it may start packets indication.
>
> Current implementation treats first operation (write 0 to ring tail)
> as signal of buffers availability and starts data transfers as soon
> as RX enable indicaton arrives.
>
> This is not correct because there is a chance that ring is still
> empty (third action not performed yet) and then memory corruption
> occures.
Any idea what the point of hw/e1000.c check_rxov is? I see nothing in
the datasheet that requires these semantics.
The Linux e1000 driver never enables the RXO (rx fifo overflow)
interrupt, only RXDMT0 (receive descriptor minimum threshold). This
means hw/e1000.c will not upset the Linux e1000 driver when
e1000_receive() gets called with check_rxov == 1 and RDH == RDT == 0.
BTW the Linux e1000 driver does not follow the sequence recommended in
the datasheet 14.4 Receive Initialization, which would avoid the weird
window of time where RDH == RDT == 0.
If we get rid of check_rxov and always check rxbuf space then we have
the correct behavior. I'm a little nervous of simply dropping it
because its purpose is unclear to me :(.
Stefan
Re: [Qemu-devel] [PATCH 1/2] Ignore RX tail kicks when RX disabled., Stefan Hajnoczi, 2012/10/18
[Qemu-devel] [PATCH 2/2] Add check_rxov into VMState., Dmitry Fleytman, 2012/10/17