linux-kernel - Re: [PATCH v9 2/4] PCI: brcmstb: Set reasonable value for internal bus timeout

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Message-ID: <20240506224508.GA1713699@bhelgaas>
Date: Mon, 6 May 2024 17:45:08 -0500
From: Bjorn Helgaas <helgaas@...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 <florian.fainelli@...adcom.com>,
	Jim Quinlan <jim2101024@...il.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 v9 2/4] PCI: brcmstb: Set reasonable value for internal
 bus timeout

On Wed, Apr 03, 2024 at 05:38:59PM -0400, Jim Quinlan wrote:
> HW initializes an internal bus timeout register to a small value for
> debugging convenience.  Set this to something reasonable, i.e. in the
> vicinity of 10 msec.
>
> Signed-off-by: Jim Quinlan <james.quinlan@...adcom.com>
> ---
>  drivers/pci/controller/pcie-brcmstb.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/drivers/pci/controller/pcie-brcmstb.c b/drivers/pci/controller/pcie-brcmstb.c
> index f9dd6622fe10..e3480ca4cd57 100644
> --- a/drivers/pci/controller/pcie-brcmstb.c
> +++ b/drivers/pci/controller/pcie-brcmstb.c
> @@ -664,6 +664,21 @@ static int brcm_pcie_enable_msi(struct brcm_pcie *pcie)
>  	return 0;
>  }
>  
> +/*
> + * An internal HW bus timer value is set to a small value for debugging
> + * convenience.  Set this to something reasonable, i.e. somewhere around
> + * 10ms.
> + */
> +static void brcm_extend_internal_bus_timeout(struct brcm_pcie *pcie, u32 nsec)
> +{
> +	/* TIMEOUT register is two registers before RGR1_SW_INIT_1 */
> +	const unsigned int REG_OFFSET = PCIE_RGR1_SW_INIT_1(pcie) - 8;
> +	u32 timeout_us = nsec / 1000;
> +
> +	/* Each unit in timeout register is 1/216,000,000 seconds */
> +	writel(216 * timeout_us, pcie->base + REG_OFFSET);
> +}
> +
>  /* The controller is capable of serving in both RC and EP roles */
>  static bool brcm_pcie_rc_mode(struct brcm_pcie *pcie)
>  {
> @@ -1059,6 +1074,9 @@ static int brcm_pcie_start_link(struct brcm_pcie *pcie)
>  		return -ENODEV;
>  	}
>  
> +	/* Extend internal bus timeout to 8ms or so */
> +	brcm_extend_internal_bus_timeout(pcie, SZ_8M);

The 216*usec is obviously determined by hardware, but the choice of
nsec for the interface, and converting to usec internally seems
arbitrary; the caller could just easily supply usec.  Or do you
envision using this interface for timeouts < 1 usec?

"SZ_8M" seems a little unusual as a time measurement and doesn't give
a hint about the units.  It's pretty common to use "8 * USEC_PER_MSEC"
or even "8 * NSEC_PER_MSEC" for things like this.

But it's fine with me as-is.

>  	if (pcie->gen)
>  		brcm_pcie_set_gen(pcie, pcie->gen);
>  
> -- 
> 2.17.1
>