linux-kernel - Re: [PATCH 4/8] PCI: tegra194: Use FIELD_GET()/FIELD

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Date:   Tue, 12 Sep 2023 11:35:52 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
CC:     <linux-pci@...r.kernel.org>, Bjorn Helgaas <helgaas@...nel.org>,
        "Lorenzo Pieralisi" <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Thierry Reding <thierry.reding@...il.com>,
        "Jonathan Hunter" <jonathanh@...dia.com>,
        <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/8] PCI: tegra194: Use FIELD_GET()/FIELD_PREP() with
 Link Width fields

On Mon, 11 Sep 2023 15:14:57 +0300
Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com> wrote:

> Use FIELD_GET() to extract PCIe Negotiated Link Width field instead of
> custom masking and shifting.
> 
> Similarly, change custom code that misleadingly used
> PCI_EXP_LNKSTA_NLW_SHIFT to prepare value for PCI_EXP_LNKCAP write
> to use FIELD_PREP() with correct field define (PCI_EXP_LNKCAP_MLW).

Excellent example for why this changes is a good cleanup beyond
reducing line lengths.  Harder to use the wrong define if you
are using one rather that two :)

Jonathan

> 
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> ---
>  drivers/pci/controller/dwc/pcie-tegra194.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-tegra194.c b/drivers/pci/controller/dwc/pcie-tegra194.c
> index 4bba31502ce1..248cd9347e8f 100644
> --- a/drivers/pci/controller/dwc/pcie-tegra194.c
> +++ b/drivers/pci/controller/dwc/pcie-tegra194.c
> @@ -9,6 +9,7 @@
>   * Author: Vidya Sagar <vidyas@...dia.com>
>   */
>  
> +#include <linux/bitfield.h>
>  #include <linux/clk.h>
>  #include <linux/debugfs.h>
>  #include <linux/delay.h>
> @@ -346,8 +347,7 @@ static void apply_bad_link_workaround(struct dw_pcie_rp *pp)
>  	 */
>  	val = dw_pcie_readw_dbi(pci, pcie->pcie_cap_base + PCI_EXP_LNKSTA);
>  	if (val & PCI_EXP_LNKSTA_LBMS) {
> -		current_link_width = (val & PCI_EXP_LNKSTA_NLW) >>
> -				     PCI_EXP_LNKSTA_NLW_SHIFT;
> +		current_link_width = FIELD_GET(PCI_EXP_LNKSTA_NLW, val);
>  		if (pcie->init_link_width > current_link_width) {
>  			dev_warn(pci->dev, "PCIe link is bad, width reduced\n");
>  			val = dw_pcie_readw_dbi(pci, pcie->pcie_cap_base +
> @@ -760,8 +760,7 @@ static void tegra_pcie_enable_system_interrupts(struct dw_pcie_rp *pp)
>  
>  	val_w = dw_pcie_readw_dbi(&pcie->pci, pcie->pcie_cap_base +
>  				  PCI_EXP_LNKSTA);
> -	pcie->init_link_width = (val_w & PCI_EXP_LNKSTA_NLW) >>
> -				PCI_EXP_LNKSTA_NLW_SHIFT;
> +	pcie->init_link_width = FIELD_GET(PCI_EXP_LNKSTA_NLW, val_w);
>  
>  	val_w = dw_pcie_readw_dbi(&pcie->pci, pcie->pcie_cap_base +
>  				  PCI_EXP_LNKCTL);
> @@ -920,7 +919,7 @@ static int tegra_pcie_dw_host_init(struct dw_pcie_rp *pp)
>  	/* Configure Max lane width from DT */
>  	val = dw_pcie_readl_dbi(pci, pcie->pcie_cap_base + PCI_EXP_LNKCAP);
>  	val &= ~PCI_EXP_LNKCAP_MLW;
> -	val |= (pcie->num_lanes << PCI_EXP_LNKSTA_NLW_SHIFT);
> +	val |= FIELD_PREP(PCI_EXP_LNKCAP_MLW, pcie->num_lanes);
>  	dw_pcie_writel_dbi(pci, pcie->pcie_cap_base + PCI_EXP_LNKCAP, val);
>  
>  	/* Clear Slot Clock Configuration bit if SRNS configuration */