linux-kernel - Re: [PATCH v2 2/8] PCI: brcmstb: Write to internal register to change link cap

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Message-ID: <20250304145425.rayj5zowyxp7s4se@thinkpad>
Date: Tue, 4 Mar 2025 20:24:25 +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>,
	Andrew Murray <amurray@...goodpenguin.co.uk>,
	Jeremy Linton <jeremy.linton@....com>,
	"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 2/8] PCI: brcmstb: Write to internal register to
 change link cap

On Fri, Feb 14, 2025 at 12:39:30PM -0500, Jim Quinlan wrote:
> The driver was mistakenly writing to a RO config-space register
> (PCI_EXP_LNKCAP).  Although harmless in this case, the proper destination
> is an internal RW register that is reflected by PCI_EXP_LNKCAP.
> 

You mean to say that writing to RO register doesn't cause any issue, but what
about the link capability not getting updated? It is a bug nevertheless.

> Fixes: c0452137034bda8f686dd9a2e167949bfffd6776 ("PCI: brcmstb: Add Broadcom STB PCIe host controller driver")
> 

Same comment as previous patch.

> 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 64a7511e66a8..98542e74aa16 100644
> --- a/drivers/pci/controller/pcie-brcmstb.c
> +++ b/drivers/pci/controller/pcie-brcmstb.c
> @@ -413,10 +413,10 @@ static int brcm_pcie_set_ssc(struct brcm_pcie *pcie)
>  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 + BRCM_PCIE_CAP_REGS + PCI_EXP_LNKCAP);
> +	u32 lnkcap = readl(pcie->base + PCIE_RC_CFG_PRIV1_LINK_CAPABILITY);
>  
>  	lnkcap = (lnkcap & ~PCI_EXP_LNKCAP_SLS) | gen;
> -	writel(lnkcap, pcie->base + BRCM_PCIE_CAP_REGS + PCI_EXP_LNKCAP);
> +	writel(lnkcap, pcie->base + PCIE_RC_CFG_PRIV1_LINK_CAPABILITY);
>  
>  	lnkctl2 = (lnkctl2 & ~0xf) | gen;
>  	writew(lnkctl2, pcie->base + BRCM_PCIE_CAP_REGS + PCI_EXP_LNKCTL2);
> -- 
> 2.43.0
> 

-- 
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