netdev - Re: [PATCH RFC 1/5] net:stmmac: set threshold/store and forward mode according to mtu size.

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Date:	Mon, 21 Oct 2013 15:28:50 +0530
From:	Rayagond K <rayagond@...avyalabs.com>
To:	Giuseppe CAVALLARO <peppe.cavallaro@...com>
Cc:	Jimmy Perchet <jimmy.perchet@...rot.com>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH RFC 1/5] net:stmmac: set threshold/store and forward mode
 according to mtu size.

On Mon, Oct 21, 2013 at 2:17 PM, Giuseppe CAVALLARO
<peppe.cavallaro@...com> wrote:
> On 10/16/2013 5:24 PM, Jimmy Perchet wrote:
>>
>> Threshold mode dma is needed on rx path if jumbo frames are expected.
>
>
> I think we should not force the threshold mode depending on the mtu.

I remember SNPS HW team suggesting me to program the rx path in
Threshold mode for jumbo frames, as it takes care of low RX FIFO size.

>
> For example, I worked on hw with rx buffers ~16KiB so able to SF
> an oversized frame.
>
> Maybe we could solve this configuration problem at platform time.
> We added the fields: force_thresh_dma_mode, force_sf_dma_mode
> to cover this scenarios. If these need to be enforced so we can
> prepare a patch.
>
> let me know
> peppe
>
>
>>
>>
>> Signed-off-by: Jimmy Perchet <jimmy.perchet@...rot.com>
>> ---
>>   drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 48
>> ++++++++++++++++-------
>>   1 file changed, 33 insertions(+), 15 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> index 8d4ccd3..170f043 100644
>> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> @@ -1222,22 +1222,40 @@ static void free_dma_desc_resources(struct
>> stmmac_priv *priv)
>>    *  Description: it sets the DMA operation mode: tx/rx DMA thresholds
>>    *  or Store-And-Forward capability.
>>    */
>> -static void stmmac_dma_operation_mode(struct stmmac_priv *priv)
>> -{
>> -       if (priv->plat->force_thresh_dma_mode)
>> -               priv->hw->dma->dma_mode(priv->ioaddr, tc, tc);
>> -       else if (priv->plat->force_sf_dma_mode || priv->plat->tx_coe) {
>> -               /*
>> -                * In case of GMAC, SF mode can be enabled
>> -                * to perform the TX COE in HW. This depends on:
>> -                * 1) TX COE if actually supported
>> -                * 2) There is no bugged Jumbo frame support
>> -                *    that needs to not insert csum in the TDES.
>> -                */
>> -               priv->hw->dma->dma_mode(priv->ioaddr, SF_DMA_MODE,
>> SF_DMA_MODE);
>> +static void stmmac_dma_operation_mode(int mtu, struct stmmac_priv *priv)
>> +{
>> +       int rx_tc, tx_tc;
>> +
>> +       /*
>> +        * In case of GMAC, SF mode can be enabled
>> +        * to perform the TX COE in HW. This depends on:
>> +        * 1) TX COE if actually supported
>> +        * 2) There is no bugged Jumbo frame support
>> +        *    that needs to not insert csum in the TDES.
>> +        */
>> +       if (priv->plat->tx_coe &&
>> +           !(priv->plat->bugged_jumbo && (mtu > ETH_DATA_LEN))) {
>>                 tc = SF_DMA_MODE;
>> +               tx_tc = SF_DMA_MODE;
>>         } else
>> -               priv->hw->dma->dma_mode(priv->ioaddr, tc, SF_DMA_MODE);
>> +               tx_tc = tc;
>> +
>> +       if (mtu > ETH_DATA_LEN && priv->hw_cap_support
>> +           && !priv->dma_cap.rxfifo_over_2048)
>> +               rx_tc = tc;
>> +       else
>> +               rx_tc = SF_DMA_MODE;
>> +
>> +       if (priv->plat->force_sf_dma_mode) {
>> +               tc = SF_DMA_MODE;
>> +               tx_tc = SF_DMA_MODE;
>> +               rx_tc = SF_DMA_MODE;
>> +       } else if (priv->plat->force_thresh_dma_mode) {
>> +               tx_tc = tc;
>> +               rx_tc = tc;
>> +       }
>> +
>> +       priv->hw->dma->dma_mode(priv->ioaddr, tx_tc, rx_tc);
>>   }
>>
>>   /**
>> @@ -1687,7 +1705,7 @@ static int stmmac_open(struct net_device *dev)
>>         stmmac_set_mac(priv->ioaddr, true);
>>
>>         /* Set the HW DMA mode and the COE */
>> -       stmmac_dma_operation_mode(priv);
>> +       stmmac_dma_operation_mode(dev->mtu, priv);
>>
>>         /* Extra statistics */
>>         memset(&priv->xstats, 0, sizeof(struct stmmac_extra_stats));
>>
>
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