Re: [PATCH v6 02/10] PCI: imx6: Add ref clock for i.MX95 PCIe

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

On Tue, Nov 19, 2024 at 05:38:30AM +0000, Hongxing Zhu wrote:
> > -----Original Message-----
> > From: Hongxing Zhu
> > Sent: 2024年11月18日 10:59
> > To: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> > Cc: l.stach@pengutronix.de; bhelgaas@google.com; lpieralisi@kernel.org;
> > kw@linux.com; robh@kernel.org; krzk+dt@kernel.org; conor+dt@kernel.org;
> > shawnguo@kernel.org; Frank Li <frank.li@nxp.com>; s.hauer@pengutronix.de;
> > festevam@gmail.com; imx@lists.linux.dev; kernel@pengutronix.de;
> > linux-pci@vger.kernel.org; linux-arm-kernel@lists.infradead.org;
> > devicetree@vger.kernel.org; linux-kernel@vger.kernel.org
> > Subject: RE: [PATCH v6 02/10] PCI: imx6: Add ref clock for i.MX95 PCIe
> > 
> > > -----Original Message-----
> > > From: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> > > Sent: 2024年11月15日 14:38
> > > To: Hongxing Zhu <hongxing.zhu@nxp.com>
> > > Cc: l.stach@pengutronix.de; bhelgaas@google.com;
> > > lpieralisi@kernel.org; kw@linux.com; robh@kernel.org;
> > > krzk+dt@kernel.org; conor+dt@kernel.org; shawnguo@kernel.org; Frank Li
> > > <frank.li@nxp.com>; s.hauer@pengutronix.de; festevam@gmail.com;
> > > imx@lists.linux.dev; kernel@pengutronix.de; linux-pci@vger.kernel.org;
> > > linux-arm-kernel@lists.infradead.org; devicetree@vger.kernel.org;
> > > linux-kernel@vger.kernel.org
> > > Subject: Re: [PATCH v6 02/10] PCI: imx6: Add ref clock for i.MX95 PCIe
> > >
> > > On Fri, Nov 01, 2024 at 03:06:02PM +0800, Richard Zhu wrote:
> > > > Add "ref" clock to enable reference clock. To avoid the DT
> > > > compatibility, i.MX95 REF clock might be optional.
> > >
> > > Your wording is not correct. Perhaps you wanted to say, "To avoid
> > > breaking DT backwards compatibility"?
> > >
> > Yes, you're right. Thanks.
> > 
> > > > Replace the
> > > > devm_clk_bulk_get() by devm_clk_bulk_get_optional() to fetch
> > > > i.MX95 PCIe optional clocks in driver.
> > > >
> > > > If use external clock, ref clock should point to external reference.
> > > >
> > > > If use internal clock, CREF_EN in LAST_TO_REG controls reference
> > > > output, which implement in drivers/clk/imx/clk-imx95-blk-ctl.c.
> > > >
> > > > Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
> > > > Reviewed-by: Frank Li <Frank.Li@nxp.com>
> > > > ---
> > > >  drivers/pci/controller/dwc/pci-imx6.c | 19 +++++++++++++------
> > > >  1 file changed, 13 insertions(+), 6 deletions(-)
> > > >
> > > > diff --git a/drivers/pci/controller/dwc/pci-imx6.c
> > > > b/drivers/pci/controller/dwc/pci-imx6.c
> > > > index 808d1f105417..bc8567677a67 100644
> > > > --- a/drivers/pci/controller/dwc/pci-imx6.c
> > > > +++ b/drivers/pci/controller/dwc/pci-imx6.c
> > > > @@ -82,6 +82,7 @@ enum imx_pcie_variants {
> > > >  #define IMX_PCIE_FLAG_HAS_SERDES		BIT(6)
> > > >  #define IMX_PCIE_FLAG_SUPPORT_64BIT		BIT(7)
> > > >  #define IMX_PCIE_FLAG_CPU_ADDR_FIXUP		BIT(8)
> > > > +#define IMX_PCIE_FLAG_CUSTOM_PME_TURNOFF	BIT(9)
> > > >
> > > >  #define imx_check_flag(pci, val)	(pci->drvdata->flags & val)
> > > >
> > > > @@ -98,6 +99,7 @@ struct imx_pcie_drvdata {
> > > >  	const char *gpr;
> > > >  	const char * const *clk_names;
> > > >  	const u32 clks_cnt;
> > > > +	const u32 clks_optional_cnt;
> > > >  	const u32 ltssm_off;
> > > >  	const u32 ltssm_mask;
> > > >  	const u32 mode_off[IMX_PCIE_MAX_INSTANCES]; @@ -1278,9
> > +1280,8
> > > @@
> > > > static int imx_pcie_probe(struct platform_device *pdev)
> > > >  	struct device_node *np;
> > > >  	struct resource *dbi_base;
> > > >  	struct device_node *node = dev->of_node;
> > > > -	int ret;
> > > > +	int ret, i, req_cnt;
> > > >  	u16 val;
> > > > -	int i;
> > > >
> > > >  	imx_pcie = devm_kzalloc(dev, sizeof(*imx_pcie), GFP_KERNEL);
> > > >  	if (!imx_pcie)
> > > > @@ -1330,7 +1331,10 @@ static int imx_pcie_probe(struct
> > > platform_device *pdev)
> > > >  		imx_pcie->clks[i].id = imx_pcie->drvdata->clk_names[i];
> > > >
> > > >  	/* Fetch clocks */
> > > > -	ret = devm_clk_bulk_get(dev, imx_pcie->drvdata->clks_cnt,
> > > imx_pcie->clks);
> > > > +	req_cnt = imx_pcie->drvdata->clks_cnt -
> > > imx_pcie->drvdata->clks_optional_cnt;
> > > > +	ret = devm_clk_bulk_get(dev, req_cnt, imx_pcie->clks);
> > > > +	ret |= devm_clk_bulk_get_optional(dev,
> > > imx_pcie->drvdata->clks_optional_cnt,
> > > > +					  imx_pcie->clks + req_cnt);
> > >
> > > Why do you need to use 'clk_bulk' API to get a single reference clock?
> > > Just use devm_clk_get_optional(dev, "ref")
> > It's easier to add more optional clks in future. I can change to use
> > devm_clk_get_optional(dev, "ref") here if you insistent.
> Since the clock fetch is not distinguished by platforms explicitly.
> devm_clk_get_optional(dev, "ref") can be used only when i.MX95 specification
>  is added.
> -       ret |= devm_clk_bulk_get_optional(dev, imx_pcie->drvdata->clks_optional_cnt,
> -                                         imx_pcie->clks + req_cnt);
>         if (ret)
>                 return ret;
> +       for (i = 0; i < imx_pcie->drvdata->clks_optional_cnt; i++) {
> +               imx_pcie->clks[req_cnt + i].clk = devm_clk_get_optional(dev,
> +                               imx_pcie->drvdata->clk_names[req_cnt + i]);
> +               if (IS_ERR(imx_pcie->clks[req_cnt + i].clk))
> +                       return PTR_ERR(imx_pcie->clks[req_cnt + i].clk);
> +       }
> 
> Or
> -       ret |= devm_clk_bulk_get_optional(dev, imx_pcie->drvdata->clks_optional_cnt,
> -                                         imx_pcie->clks + req_cnt);
>         if (ret)
>                 return ret;
> +       if (imx_pcie->drvdata->variant == IMX95) {

Why do you need this check? If there is no clock, devm_clk_get_optional() will
return NULL, so you can just do IS_ERR() without any checks.

- Mani

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