linux-kernel - Re: [PATCH net v3] net: stmmac: update Rx clk divider for 10M SGMII

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Message-ID: <5luxwdjyzkg5o6w27mqixggr65ebosnn53vaqrbtsclfudet4v@kse23pgyj7ld>
Date:   Fri, 8 Dec 2023 20:24:44 -0800
From:   Bjorn Andersson <andersson@...nel.org>
To:     Sneh Shah <quic_snehshah@...cinc.com>
Cc:     Vinod Koul <vkoul@...nel.org>,
        Bhupesh Sharma <bhupesh.sharma@...aro.org>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        netdev@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kernel@...cinc.com, Andrew Halaney <ahalaney@...hat.com>
Subject: Re: [PATCH net v3] net: stmmac: update Rx clk divider for 10M SGMII

On Fri, Dec 08, 2023 at 11:55:02AM +0530, Sneh Shah wrote:
> SGMII 10MBPS mode needs RX clock divider to avoid drops in Rx.
> Update configure SGMII function with rx clk divider programming.

Are you trying saying that the RX clock is completely wrong in 10MBps
mode? Or is the RX clock good, but without some division of some other
clock signal you loose some packets now and then?

Please write your commit message such that it describe the actual
problem you're having. This will help others to know if this fix is
applicable to some issue they are seeing on their hardware, now and in
the future.

> 
> Fixes: 463120c31c58 ("net: stmmac: dwmac-qcom-ethqos: add support for SGMII")
> Signed-off-by: Sneh Shah <quic_snehshah@...cinc.com>
> ---
> v3 changelog:
> - Added comment to explain why MAC needs to be reconfigured for SGMII
> v2 changelog:
> - Use FIELD_PREP to prepare bifield values in place of GENMASK
> - Add fixes tag
> ---
>  drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c
> index d3bf42d0fceb..ab2245995bc6 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c
> @@ -34,6 +34,7 @@
>  #define RGMII_CONFIG_LOOPBACK_EN		BIT(2)
>  #define RGMII_CONFIG_PROG_SWAP			BIT(1)
>  #define RGMII_CONFIG_DDR_MODE			BIT(0)
> +#define RGMII_CONFIG_SGMII_CLK_DVDR		GENMASK(18, 10)

This new bitfield overlaps with existing fields, is it the same
register? Did the fields move? Is it applicable to all versions?

What will existing writes to RGMII_IO_MACRO_CONFIG do to this new
layout? What will the new write do to hardware with the existing field
layout?

>  
>  /* SDCC_HC_REG_DLL_CONFIG fields */
>  #define SDCC_DLL_CONFIG_DLL_RST			BIT(30)
> @@ -598,6 +599,9 @@ static int ethqos_configure_rgmii(struct qcom_ethqos *ethqos)
>  	return 0;
>  }
>  
> +/* On interface toggle MAC registetrs gets reset.
> + * Configure MAC block for SGMII on ethernet phy link up
> + */
>  static int ethqos_configure_sgmii(struct qcom_ethqos *ethqos)
>  {
>  	int val;
> @@ -617,6 +621,9 @@ static int ethqos_configure_sgmii(struct qcom_ethqos *ethqos)
>  	case SPEED_10:
>  		val |= ETHQOS_MAC_CTRL_PORT_SEL;
>  		val &= ~ETHQOS_MAC_CTRL_SPEED_MODE;
> +		rgmii_updatel(ethqos, RGMII_CONFIG_SGMII_CLK_DVDR,
> +			      FIELD_PREP(RGMII_CONFIG_SGMII_CLK_DVDR, 0x31),

Is this just a magic constant, or does 0x31 of some convenient unit?
Could we give it name/define?

Regards,
Bjorn

> +			      RGMII_IO_MACRO_CONFIG);
>  		break;
>  	}
>  
> -- 
> 2.17.1
> 
>