linux-kernel - Re: [PATCH v6 3/5] PCI: brcmstb: Set higher value for internal bus timeout

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Message-ID: <ZMN/x+Iuac6qLSnd@lpieralisi>
Date:   Fri, 28 Jul 2023 10:43:51 +0200
From:   Lorenzo Pieralisi <lpieralisi@...nel.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>,
        Phil Elwell <phil@...pberrypi.com>,
        bcm-kernel-feedback-list@...adcom.com,
        Florian Fainelli <f.fainelli@...il.com>,
        Jim Quinlan <jim2101024@...il.com>,
        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 v6 3/5] PCI: brcmstb: Set higher value for internal bus
 timeout

On Fri, Jun 23, 2023 at 10:40:56AM -0400, Jim Quinlan wrote:
> During long periods of the PCIe RC HW being in an L1SS sleep state, there
> may be a timeout on an internal bus access, even though there may not be
> any PCIe access involved.  Such a timeout will cause a subsequent CPU
> abort.
> 
> So, when "brcm,enable-l1ss" is observed, we increase the timeout value to
> four seconds instead of using its HW default.
> 
> Signed-off-by: Jim Quinlan <james.quinlan@...adcom.com>
> Tested-by: Florian Fainelli <f.fainelli@...il.com>
> ---
>  drivers/pci/controller/pcie-brcmstb.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/drivers/pci/controller/pcie-brcmstb.c b/drivers/pci/controller/pcie-brcmstb.c
> index d30636a725d7..fe0415a98c63 100644
> --- a/drivers/pci/controller/pcie-brcmstb.c
> +++ b/drivers/pci/controller/pcie-brcmstb.c
> @@ -1034,6 +1034,21 @@ static int brcm_pcie_setup(struct brcm_pcie *pcie)
>  	return 0;
>  }
>  
> +/*
> + * This extends the timeout period for an access to an internal bus.  This
> + * access timeout may occur during L1SS sleep periods even without the
> + * presence of a PCIe access.
> + */
> +static void brcm_extend_rbus_timeout(struct brcm_pcie *pcie)
> +{
> +	/* TIMEOUT register is two registers before RGR1_SW_INIT_1 */
> +	const unsigned int REG_OFFSET = PCIE_RGR1_SW_INIT_1(pcie) - 8;

Nit: you could define an offset for the TIMEOUT register, if that makes
it any cleaner, up to you.

> +	u32 timeout_us = 4000000; /* 4 seconds, our setting for L1SS */

It would be useful to describe why this has to be 4 seconds in case
someone in the future will have to change it.

Thanks,
Lorenzo

> +	/* Each unit in timeout register is 1/216,000,000 seconds */
> +	writel(216 * timeout_us, pcie->base + REG_OFFSET);
> +}
> +
>  static void brcm_config_clkreq(struct brcm_pcie *pcie)
>  {
>  	bool l1ss = of_property_read_bool(pcie->np, "brcm,enable-l1ss");
> @@ -1059,6 +1074,7 @@ static void brcm_config_clkreq(struct brcm_pcie *pcie)
>  		 * of 400ns, as specified in 3.2.5.2.2 of the PCI Express
>  		 * Mini CEM 2.0 specification.
>  		 */
> +		brcm_extend_rbus_timeout(pcie);
>  		clkreq_set |= PCIE_MISC_HARD_PCIE_HARD_DEBUG_L1SS_ENABLE_MASK;
>  		dev_info(pcie->dev, "bi-dir CLKREQ# for L1SS power savings");
>  	} else {
> -- 
> 2.17.1
>