linux-kernel - Re: [PATCH 2/2] PCI: amlogic: Use PCIe pll gate when available

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Message-ID: <20191209110314.GQ18399@e119886-lin.cambridge.arm.com>
Date:   Mon, 9 Dec 2019 11:03:15 +0000
From:   Andrew Murray <andrew.murray@....com>
To:     Remi Pommarel <repk@...plefau.lt>
Cc:     Neil Armstrong <narmstrong@...libre.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        Kevin Hilman <khilman@...libre.com>,
        Yue Wang <yue.wang@...ogic.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        linux-amlogic@...ts.infradead.org, linux-clk@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org
Subject: Re: [PATCH 2/2] PCI: amlogic: Use PCIe pll gate when available

On Sun, Dec 08, 2019 at 10:03:20PM +0100, Remi Pommarel wrote:
> In order to get PCIe working reliably on some AXG platforms, PCIe pll
> cml needs to be enabled. This is done by using the PCIE_PLL_CML_ENABLE
> clock gate.

s/cml/CML/

In addition to Jerome's feedback - it would also be helpful to explain
when CML outputs should be enabled, i.e. which platforms and why those
ones?

> 
> This clock gate is optional, so do not fail if it is missing in the
> devicetree.

If certain platforms require PCIE_PLL_CML_ENABLE to work reliably and
thus the clock is specified in the device tree - then surely if there
is an error in enabling the clock we should fail? I.e. should you only
ignore -ENOENT here?

Thanks,

Andrew Murray

> 
> Signed-off-by: Remi Pommarel <repk@...plefau.lt>
> ---
>  drivers/pci/controller/dwc/pci-meson.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pci-meson.c b/drivers/pci/controller/dwc/pci-meson.c
> index 3772b02a5c55..32b70ea9a426 100644
> --- a/drivers/pci/controller/dwc/pci-meson.c
> +++ b/drivers/pci/controller/dwc/pci-meson.c
> @@ -89,6 +89,7 @@ struct meson_pcie_clk_res {
>  	struct clk *mipi_gate;
>  	struct clk *port_clk;
>  	struct clk *general_clk;
> +	struct clk *pll_cml_gate;
>  };
>  
>  struct meson_pcie_rc_reset {
> @@ -300,6 +301,10 @@ static int meson_pcie_probe_clocks(struct meson_pcie *mp)
>  	if (IS_ERR(res->clk))
>  		return PTR_ERR(res->clk);
>  
> +	res->pll_cml_gate = meson_pcie_probe_clock(dev, "pll_cml_en", 0);
> +	if (IS_ERR(res->pll_cml_gate))
> +		res->pll_cml_gate = NULL;
> +
>  	return 0;
>  }
>  
> -- 
> 2.24.0
>