Re: [PATCH net] net: stmmac: First Queue must always be in DCB mode

[Jose Abreu <Jose.Abreu@synopsys.com>]

On 26-10-2017 15:44, Bhadram Varka wrote:
> Hi Jose,
>
>> -----Original Message-----
>> From: Jose Abreu [mailto:Jose.Abreu@synopsys.com]
>> Sent: Thursday, October 26, 2017 5:19 PM
>> To: Bhadram Varka <vbhadram@nvidia.com>; netdev@vger.kernel.org;
>> linux-kernel@vger.kernel.org
>> Cc: Joao Pinto <Joao.Pinto@synopsys.com>; David S. Miller
>> <davem@davemloft.net>; Giuseppe Cavallaro <peppe.cavallaro@st.com>;
>> Alexandre Torgue <alexandre.torgue@st.com>
>> Subject: Re: [PATCH net] net: stmmac: First Queue must always be in DCB
>> mode
>>
>> Hi Bhadram,
>>
>> On 26-10-2017 11:51, Bhadram Varka wrote:
>>> Hi Jose,
>>>
>>>> -----Original Message-----
>>>> From: netdev-owner@vger.kernel.org [mailto:netdev-
>>>> owner@vger.kernel.org] On Behalf Of Jose Abreu
>>>> Sent: Thursday, October 26, 2017 2:37 PM
>>>> To: netdev@vger.kernel.org; linux-kernel@vger.kernel.org
>>>> Cc: Jose Abreu <Jose.Abreu@synopsys.com>; Joao Pinto
>>>> <Joao.Pinto@synopsys.com>; David S. Miller <davem@davemloft.net>;
>>>> Giuseppe Cavallaro <peppe.cavallaro@st.com>; Alexandre Torgue
>>>> <alexandre.torgue@st.com>
>>>> Subject: [PATCH net] net: stmmac: First Queue must always be in DCB
>>>> mode
>>>>
>>>> According to DWMAC databook the first queue operating mode must
>>>> always be in DCB.
>>>>
>>>> As MTL_QUEUE_DCB = 1, we need to always set the first queue operating
>>>> mode to DCB otherwise driver will think that queue is in AVB mode
>>>> (because MTL_QUEUE_AVB = 0).
>>>>
>>>> Signed-off-by: Jose Abreu <joabreu@synopsys.com>
>>>> Cc: Joao Pinto <jpinto@synopsys.com>
>>>> Cc: David S. Miller <davem@davemloft.net>
>>>> Cc: Giuseppe Cavallaro <peppe.cavallaro@st.com>
>>>> Cc: Alexandre Torgue <alexandre.torgue@st.com>
>>>> ---
>>>>  drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c | 7 +++++++
>>>>  1 file changed, 7 insertions(+)
>>>>
>>>> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
>>>> b/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
>>>> index 21f59fe..603225b 100644
>>>> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
>>>> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
>>>> @@ -150,6 +150,13 @@ static void stmmac_mtl_setup(struct
>>>> platform_device *pdev,
>>>>  	plat->rx_queues_to_use = 1;
>>>>  	plat->tx_queues_to_use = 1;
>>>>
>>>> +	/* First Queue must always be in DCB mode. As MTL_QUEUE_DCB =
>>>> 1 we need
>>>> +	 * to always set this, otherwise Queue will be classified as AVB
>>>> +	 * (because MTL_QUEUE_AVB = 0).
>>>> +	 */
>>> Its better if we can check whether IP HW features (register - 0x120)
>> supports the DCB or not. If yes, then set the DCB mode.
>>> There is possibility that DCB feature not enable for few of the Synopsys
>> IP's.
>>
>> A queue can either be in Generic/DCB or AVB mode. The sequence to enable
>> a DCB or a Generic queue is the same so there is no need to check for DCB
>> capability in HW.
> Point is that we don't have DCB enabled for the IP. 
>
> From your point it will work in Generic (legacy) mode if we set DCB filed. If this is the understanding then we are fine.

Yes, thats true. Generic and DCB have the same configuration.

Best Regards,
Jose Miguel Abreu

>
> Thanks,
> Bhadram.