netdev - Re: [PATCH] mvneta driver XDP fixes armhf

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Date:   Wed, 22 Jan 2020 23:57:40 +0100
From:   "lorenzo.bianconi@...hat.com" <lorenzo.bianconi@...hat.com>
To:     Sven Auhagen <sven.auhagen@...eatech.de>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "thomas.petazzoni@...tlin.com" <thomas.petazzoni@...tlin.com>,
        "brouer@...hat.com" <brouer@...hat.com>,
        "ilias.apalodimas@...aro.org" <ilias.apalodimas@...aro.org>,
        "matteo.croce@...hat.com" <matteo.croce@...hat.com>,
        "mw@...ihalf.com" <mw@...ihalf.com>,
        "jakub.kicinski@...ronome.com" <jakub.kicinski@...ronome.com>
Subject: Re: [PATCH] mvneta driver XDP fixes armhf

Hi Sven,

> Recently XDP Support was added to the mvneta driver for software buffer management.
> I tested XDP with my armada 388 board. It has hardware buffer management defined in the device tree file.
> I disabled the mvneta_bm module to test XDP.
> 
> I found multiple problems.
> 
> 1. With hardware buffer management enabled and mvneta_bm disabled the rx_offset was set to 0 with armhf (32 bit) which leads to no headroom in XDP and therefore the XDP Redirect did not work.
> 2. Removing the hardware buffer management from the device tree file completely made the mvneta driver unusable as it did not work anymore.

Do you mean removing 'buffer-manager' property from the device tree?

> 
> After some debugging I found out that xdp->data = data + pp->rx_offset_correction + MVNETA_MH_SIZE;  has to be xdp->data = data + pp->rx_offset_correction; if pp->rx_offset_correction > 0.
> I am not sure why and I am looking for help if someone is seeing the same on an arm64 board.

Are you sure the hw does not insert the mvneta header before the data? It seems
to me that it is added even for hw buffer devices (according to the code).

> 
> Attached is a patch that fixes the problem on my armhf platform, as said I am not sure if this is a universal fix or armhf only.
> 
> Any feedback is appreciated.
> 
> Signed-off-by: Sven Auhagen <sven.auhagen@...eatech.de>
> 
> --- a/drivers/net/ethernet/marvell/mvneta.c2020-01-22 08:44:05.611395960 +0000
> +++ b/drivers/net/ethernet/marvell/mvneta.c2020-01-22 08:59:27.053739433 +0000
> @@ -2158,7 +2158,7 @@ mvneta_swbm_rx_frame(struct mvneta_port
>  prefetch(data);
> 
>  xdp->data_hard_start = data;
> -xdp->data = data + pp->rx_offset_correction + MVNETA_MH_SIZE;
> +xdp->data = data + pp->rx_offset_correction;

This will break XDP support for 'real' sw buffer devices like Espressobin.

Regards,
Lorenzo

>  xdp->data_end = xdp->data + data_len;
>  xdp_set_data_meta_invalid(xdp);
> 
> @@ -4960,7 +4960,8 @@ static int mvneta_probe(struct platform_
>   * NET_SKB_PAD, exceeds 64B. It should be 64B for 64-bit
>   * platforms and 0B for 32-bit ones.
>   */
> -pp->rx_offset_correction = max(0,
> +if (pp->bm_priv)
> +pp->rx_offset_correction = max(0,
>         NET_SKB_PAD -
>         MVNETA_RX_PKT_OFFSET_CORRECTION);
>  }
> 
> 
> 
> 
> +++ Voleatech auf der E-World, 11. bis 13. Februar 2020, Halle 5, Stand 521 +++
> 
> Beste Grüße/Best regards
> 
> Sven Auhagen
> Dipl. Math. oec., M.Sc.
> Voleatech GmbH
> HRB: B 754643
> USTID: DE303643180
> Grathwohlstr. 5
> 72762 Reutlingen
> Tel: +49 7121539550
> Fax: +49 7121539551
> E-Mail: sven.auhagen@...eatech.de
> www.voleatech.de<https://www.voleatech.de>
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