linux-kernel - Re: [PATCH v2 3/8] PCI: brcmstb: Do not assume that reg field starts at LSB

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Message-ID: <20250304145724.itrzj6wnflxxf3up@thinkpad>
Date: Tue, 4 Mar 2025 20:27:24 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Jim Quinlan <james.quinlan@...adcom.com>
Cc: linux-pci@...r.kernel.org, Nicolas Saenz Julienne <nsaenz@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Cyril Brulebois <kibi@...ian.org>,
	Stanimir Varbanov <svarbanov@...e.de>,
	bcm-kernel-feedback-list@...adcom.com, jim2101024@...il.com,
	Florian Fainelli <florian.fainelli@...adcom.com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Rob Herring <robh@...nel.org>,
	"moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" <linux-rpi-kernel@...ts.infradead.org>,
	"moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" <linux-arm-kernel@...ts.infradead.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/8] PCI: brcmstb: Do not assume that reg field starts
 at LSB

On Fri, Feb 14, 2025 at 12:39:31PM -0500, Jim Quinlan wrote:
> When setting a register field it was assumed that the field started at the

s/a register field/LNKCAP and LNKCTL2 register fields,

> lsb of the register.  Although the masks do indeed start at the lsb, and
> this will probably not change, it is prudent to use a method that makes no
> assumption about the mask's placement in the register.
> 
> The uXXp_replace_bits() calls are used since they are already prevalent
> in this driver.
> 
> Signed-off-by: Jim Quinlan <james.quinlan@...adcom.com>

Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>

- Mani

> ---
>  drivers/pci/controller/pcie-brcmstb.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/controller/pcie-brcmstb.c b/drivers/pci/controller/pcie-brcmstb.c
> index 98542e74aa16..e0b20f58c604 100644
> --- a/drivers/pci/controller/pcie-brcmstb.c
> +++ b/drivers/pci/controller/pcie-brcmstb.c
> @@ -415,10 +415,10 @@ static void brcm_pcie_set_gen(struct brcm_pcie *pcie, int gen)
>  	u16 lnkctl2 = readw(pcie->base + BRCM_PCIE_CAP_REGS + PCI_EXP_LNKCTL2);
>  	u32 lnkcap = readl(pcie->base + PCIE_RC_CFG_PRIV1_LINK_CAPABILITY);
>  
> -	lnkcap = (lnkcap & ~PCI_EXP_LNKCAP_SLS) | gen;
> +	u32p_replace_bits(&lnkcap, gen, PCI_EXP_LNKCAP_SLS);
>  	writel(lnkcap, pcie->base + PCIE_RC_CFG_PRIV1_LINK_CAPABILITY);
>  
> -	lnkctl2 = (lnkctl2 & ~0xf) | gen;
> +	u16p_replace_bits(&lnkctl2, gen, PCI_EXP_LNKCTL2_TLS);
>  	writew(lnkctl2, pcie->base + BRCM_PCIE_CAP_REGS + PCI_EXP_LNKCTL2);
>  }
>  
> -- 
> 2.43.0
> 

-- 
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