Subject: Re: [PATCH net-next v2 3/3] net: stmmac: Configure AXI on Tegra234 MGBE

From: "Thierry Reding" <[email-masked]>
Date: Tue, 13 Feb 2024 16:51:34 +0100

On Mon Feb 5, 2024 at 1:44 AM CET, Serge Semin wrote:
> On Fri, Feb 02, 2024 at 12:53:35PM +0100, Thierry Reding wrote:
> > From: Thierry Reding <[email-masked]>
> > 
> > Allow the device to use bursts and increase the maximum number of
> > outstanding requests to improve performance. Measurements show an
> > increase in throughput of around 5x on a 1 Gbps link.
> > 
> > Signed-off-by: Thierry Reding <[email-masked]>
> > ---
> >  drivers/net/ethernet/stmicro/stmmac/dwmac-tegra.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> > 
> > diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-tegra.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-tegra.c
> > index bab57d1675df..b6bfa48f279d 100644
> > --- a/drivers/net/ethernet/stmicro/stmmac/dwmac-tegra.c
> > +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-tegra.c
> > @@ -199,6 +199,12 @@ static void mgbe_uphy_lane_bringup_serdes_down(struct net_device *ndev, void *mg
> >  	writel(value, mgbe->xpcs + XPCS_WRAP_UPHY_RX_CONTROL);
> >  }
> >  
> > +static const struct stmmac_axi tegra234_mgbe_axi = {
> > +	.axi_wr_osr_lmt = 63,
> > +	.axi_rd_osr_lmt = 63,
> > +	.axi_blen = { 256, },
> > +};
> > +
> >  static int tegra_mgbe_probe(struct platform_device *pdev)
> >  {
> >  	struct plat_stmmacenet_data *plat;
> > @@ -284,6 +290,9 @@ static int tegra_mgbe_probe(struct platform_device *pdev)
> >  	if (err < 0)
> >  		goto disable_clks;
> >  
> > +	/* setup default AXI configuration */
> > +	res.axi = &tegra234_mgbe_axi;
> > +
> >  	plat = devm_stmmac_probe_config_dt(pdev, &res);
> >  	if (IS_ERR(plat)) {
> >  		err = PTR_ERR(plat);
>
> The entire series can be converted to just a few lines of change:

Sorry for the delay, I missed this reply.

>  	plat = devm_stmmac_probe_config_dt(pdev, res.mac);
>  	if (IS_ERR(plat)) {
>  		err = PTR_ERR(plat);
>  		goto disable_clks;
>  	}
> +
> +	if (IS_ERR_OR_NULL(plat->axi)) {
> +		plat->axi = devm_kzalloc(&pdev->dev, sizeof(*axi), GFP_KERNEL);
> +		if (!plat->axi) {
> +			ret = -ENOMEM;
> +			goto disable_clks;
> +		}
> +	} /* else memset plat->axi with zeros if you wish */
> +
> +	plat->axi->axi_wr_osr_lmt = 63;
> +	plat->axi->axi_rd_osr_lmt = 63;
> +	plat->axi->axi_blen[0] = 256;
>  
>  	plat->has_xgmac = 1;
>  	plat->flags |= STMMAC_FLAG_TSO_EN;
>  	plat->pmt = 1;
>
> Please don't overcomplicate the already overcomplicated driver with a
> functionality which can be reached by the default one. In this case
> the easiest way is to let the generic code work and then
> override/replace/fix/etc the retrieved values. Thus there won't be
> need in adding the redundant functionality and keep the generic
> DT-platform code a bit simpler to read.

I'm not sure I understand how this is overcomplicating things. The code
is pretty much unchanged, except that the AXI configuration can now have
driver-specified defaults before the DT is parsed. Perhaps I need to add
comments to make that a bit clearer?

While your version is certainly simpler it has the drawback that it no
longer allows the platform defaults to be overridden in device tree. I
would prefer if the defaults can be derived from the compatible string
but if need be for those defaults to still be overridable from device
tree.

Thierry