netdev - Re: [PATCH] net: stmmac: enable tx queue 0 for gmac4 IPs synthesized with multiple TX queues

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Date:   Fri, 25 Nov 2016 13:10:24 +0100
From:   Niklas Cassel <niklas.cassel@...s.com>
To:     Alexandre Torgue <alexandre.torgue@...com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>
CC:     <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: stmmac: enable tx queue 0 for gmac4 IPs synthesized
 with multiple TX queues

On 11/24/2016 07:11 PM, Alexandre Torgue wrote:
> Hi Niklas,

Hello Alexandre

>
> On 11/24/2016 03:36 PM, Niklas Cassel wrote:
>> From: Niklas Cassel <niklas.cassel@...s.com>
>>
>> The dwmac4 IP can synthesized with 1-8 number of tx queues.
>> On an IP synthesized with DWC_EQOS_NUM_TXQ > 1, all txqueues are disabled
>> by default. For these IPs, the bitfield TXQEN is R/W.
>>
>> Always enable tx queue 0. The write will have no effect on IPs synthesized
>> with DWC_EQOS_NUM_TXQ == 1.
>>
>> The driver does still not utilize more than one tx queue in the IP.
>>
>> Signed-off-by: Niklas Cassel <niklas.cassel@...s.com>
>> ---
>>  drivers/net/ethernet/stmicro/stmmac/dwmac4.h     |  3 +++
>>  drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c | 12 +++++++++++-
>>  2 files changed, 14 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac4.h b/drivers/net/ethernet/stmicro/stmmac/dwmac4.h
>> index 6f4f5ce25114..3e8d4fefa5e0 100644
>> --- a/drivers/net/ethernet/stmicro/stmmac/dwmac4.h
>> +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac4.h
>> @@ -155,8 +155,11 @@ enum power_event {
>>  #define MTL_CHAN_RX_DEBUG(x)        (MTL_CHANX_BASE_ADDR(x) + 0x38)
>>
>>  #define MTL_OP_MODE_RSF            BIT(5)
>> +#define MTL_OP_MODE_TXQEN        BIT(3)
>>  #define MTL_OP_MODE_TSF            BIT(1)
>>
>> +#define MTL_OP_MODE_TQS_MASK        GENMASK(24, 16)
>> +
>>  #define MTL_OP_MODE_TTC_MASK        0x70
>>  #define MTL_OP_MODE_TTC_SHIFT        4
>>
>> diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c b/drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c
>> index 116151cd6a95..577316de6ba8 100644
>> --- a/drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c
>> +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c
>> @@ -213,7 +213,17 @@ static void dwmac4_dma_chan_op_mode(void __iomem *ioaddr, int txmode,
>>          else
>>              mtl_tx_op |= MTL_OP_MODE_TTC_512;
>>      }
>> -
>> +    /* For an IP with DWC_EQOS_NUM_TXQ == 1, the fields TXQEN and TQS are RO
>> +     * with reset values: TXQEN on, TQS == DWC_EQOS_TXFIFO_SIZE.
>> +     * For an IP with DWC_EQOS_NUM_TXQ > 1, the fields TXQEN and TQS are R/W
>> +     * with reset values: TXQEN off, TQS 256 bytes.
>> +     *
>> +     * Write the bits in both cases, since it will have no effect when RO.
>> +     * For DWC_EQOS_NUM_TXQ > 1, the top bits in MTL_OP_MODE_TQS_MASK might
>> +     * be RO, however, writing the whole TQS field will result in a value
>> +     * equal to DWC_EQOS_TXFIFO_SIZE, just like for DWC_EQOS_NUM_TXQ == 1.
>> +     */
>> +    mtl_tx_op |= MTL_OP_MODE_TXQEN | MTL_OP_MODE_TQS_MASK;
>
> Your patch sounds good. Just one question:
>
> In synopsys databook I use, I see that MTL_OP_MODE_TXQEN for channel 2 can take several values "disabled / enabled / Enabled in AV mode":
>
> Transmit Queue Enable
> This field is used to enable/disable the transmit queue 1. 00 R/W
> ■ 2'b00 - Not enabled
> ■ 2'b01 - Enable in AV mode (Reserved when Enable Audio Video
> Bridging is not selected while configuring the core)
> ■ 2'b10 - Enabled
> ■ 2'b11 - Reserved
>
> Do you plan to manage av mode in a future patch ?

We are not planning on using the AV mode.
We will probably not use TXQ1 at all.

I noticed that the MAC_HW_Feature2 Register actually has a TXQCNT field.
It is currently saved in priv->dma_cap.number_tx_channel.
If you prefer, I could do a patch V2 where we only set the bits if
priv->dma_cap.number_tx_channel > 1

However, I don't think the current patch is too bad either, since the bits
are RO when number_tx_channel == 1.


>
> Regards
> Alex
>
>>      writel(mtl_tx_op, ioaddr +  MTL_CHAN_TX_OP_MODE(channel));
>>
>>      mtl_rx_op = readl(ioaddr + MTL_CHAN_RX_OP_MODE(channel));
>>