Re: [PATCH v2] hw/net: fsl_etsec: Reverse the RCTRL.RSF logic

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Feb 09, 2021 at 09:22:41AM +0800, Bin Meng wrote:
> From: Bin Meng <bin.meng@windriver.com>
> 
> Per MPC8548ERM [1] chapter 14.5.3.4.1:
> 
> When RCTRL.RSF is 1, frames less than 64 bytes are accepted upon
> a DA match. But currently QEMU does the opposite.
> 
> When RCTRL.RSF is 0, short frames are silently dropped, however
> we cannot drop such frames in QEMU as of today, due to both slirp
> and tap networking do not pad short frames (e.g.: an ARP packet)
> to the minimum frame size of 60 bytes.
> 
> If eTSEC is programmed to reject short frames, ARP requests will be
> dropped, preventing the guest from becoming visible on the network.
> 
> The same issue was reported on e1000 and vmxenet3 before, see:
> 
> commit 78aeb23eded2 ("e1000: Pad short frames to minimum size (60 bytes)")
> commit 40a87c6c9b11 ("vmxnet3: Pad short frames to minimum size (60 bytes)")
> 
> Ideally this should be fixed on the slirp/tap networking side to
> pad short frames to the minimum frame length, but I am not sure
> whether that's doable.
> 
> This commit reverses the RCTRL.RSF testing logic to match the spec.
> The log message is updated to mention the reject short frames
> functionality is unimplemented.
> 
> [1] https://www.nxp.com/docs/en/reference-manual/MPC8548ERM.pdf
> 
> Fixes: eb1e7c3e5146 ("Add Enhanced Three-Speed Ethernet Controller (eTSEC)")
> Signed-off-by: Bin Meng <bin.meng@windriver.com>

Applied to ppc-for-6.0.

Thanks for the excellent commit message with the links to the relevant
documentation.

> 
> ---
> 
> Changes in v2:
> - rewrite the commit message and reverse the RCTRL.RSF test logic
> 
>  hw/net/fsl_etsec/rings.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/net/fsl_etsec/rings.c b/hw/net/fsl_etsec/rings.c
> index 121415a..f89aa7f 100644
> --- a/hw/net/fsl_etsec/rings.c
> +++ b/hw/net/fsl_etsec/rings.c
> @@ -502,10 +502,17 @@ ssize_t etsec_rx_ring_write(eTSEC *etsec, const uint8_t *buf, size_t size)
>          return -1;
>      }
>  
> -    if ((etsec->regs[RCTRL].value & RCTRL_RSF) && (size < 60)) {
> +    /*
> +     * Both slirp and tap networking do not pad short frames
> +     * (e.g.: an ARP packet) to the minimum frame size of 60 bytes.
> +     *
> +     * If eTSEC is programmed to reject short frames, ARP requests
> +     * will be dropped, preventing the guest from becoming visible
> +     * on the network.
> +     */
> +    if (!(etsec->regs[RCTRL].value & RCTRL_RSF) && (size < 60)) {
>          /* CRC is not in the packet yet, so short frame is below 60 bytes */
> -        RING_DEBUG("%s: Drop short frame\n", __func__);
> -        return -1;
> +        RING_DEBUG("%s: Drop short frame not implemented\n", __func__);
>      }
>  
>      rx_init_frame(etsec, buf, size);

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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