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Message-ID: <CA+-6iNxsnj7-Nsy4Q6wFbiF-a6BwfYeTnCqdg1sAUXPCpyaMzg@mail.gmail.com>
Date: Thu, 7 Aug 2025 14:03:18 -0400
From: Jim Quinlan <james.quinlan@...adcom.com>
To: Bjorn Helgaas <helgaas@...nel.org>
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>, bcm-kernel-feedback-list@...adcom.com,
jim2101024@...il.com, Florian Fainelli <florian.fainelli@...adcom.com>,
Lorenzo Pieralisi <lpieralisi@...nel.org>, Krzysztof Wilczyński <kwilczynski@...nel.org>,
Manivannan Sadhasivam <mani@...nel.org>, 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 1/2] PCI: brcmstb: Add a way to indicate if PCIe bridge is active
On Wed, Aug 6, 2025 at 3:14 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> On Fri, Jun 13, 2025 at 06:08:42PM -0400, Jim Quinlan wrote:
> > In a future commit, a new handler will be introduced that in part does
> > reads and writes to some of the PCIe registers. When this handler is
> > invoked, it is paramount that it does not do these register accesses when
> > the PCIe bridge is inactive, as this will cause CPU abort errors.
> >
> > To solve this we keep a spinlock that guards a variable which indicates
> > whether the bridge is on or off. When the bridge is on, access of the PCIe
> > HW registers may proceed.
> >
> > Since there are multiple ways to reset the bridge, we introduce a general
> > function to obtain the spinlock, call the specific function that is used
> > for the specific SoC, sets the bridge active indicator variable, and
> > releases the spinlock.
> >
> > Signed-off-by: Jim Quinlan <james.quinlan@...adcom.com>
> > ---
> > drivers/pci/controller/pcie-brcmstb.c | 40 +++++++++++++++++++++++----
> > 1 file changed, 35 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/pci/controller/pcie-brcmstb.c b/drivers/pci/controller/pcie-brcmstb.c
> > index 92887b394eb4..400854c893d8 100644
> > --- a/drivers/pci/controller/pcie-brcmstb.c
> > +++ b/drivers/pci/controller/pcie-brcmstb.c
> > @@ -29,6 +29,7 @@
> > #include <linux/reset.h>
> > #include <linux/sizes.h>
> > #include <linux/slab.h>
> > +#include <linux/spinlock.h>
> > #include <linux/string.h>
> > #include <linux/types.h>
> >
> > @@ -254,6 +255,7 @@ struct pcie_cfg_data {
> > int (*perst_set)(struct brcm_pcie *pcie, u32 val);
> > int (*bridge_sw_init_set)(struct brcm_pcie *pcie, u32 val);
> > int (*post_setup)(struct brcm_pcie *pcie);
> > + bool has_err_report;
>
> It doesn't look worth it to me to add this. It only avoids locking in
> a non-performance path.
>
> > };
> >
> > struct subdev_regulators {
> > @@ -299,6 +301,8 @@ struct brcm_pcie {
> > struct subdev_regulators *sr;
> > bool ep_wakeup_capable;
> > const struct pcie_cfg_data *cfg;
> > + bool bridge_on;
> > + spinlock_t bridge_lock;
> > };
> >
> > static inline bool is_bmips(const struct brcm_pcie *pcie)
> > @@ -306,6 +310,24 @@ static inline bool is_bmips(const struct brcm_pcie *pcie)
> > return pcie->cfg->soc_base == BCM7435 || pcie->cfg->soc_base == BCM7425;
> > }
> >
> > +static inline int brcm_pcie_bridge_sw_init_set(struct brcm_pcie *pcie, u32 val)
> > +{
> > + unsigned long flags;
> > + int ret;
> > +
> > + if (pcie->cfg->has_err_report)
> > + spin_lock_irqsave(&pcie->bridge_lock, flags);
> > +
> > + ret = pcie->cfg->bridge_sw_init_set(pcie, val);
> > + if (ret)
> > + pcie->bridge_on = !val;
>
> AFAICT, .bridge_sw_init_set(1) asserts reset, .bridge_sw_init_set(0)
> deasserts reset, and it returns 0 for success, so I'm confused about
> this. If either assert or deassert failed (ret != 0), I guess we
> don't know the state of the bridge and can't assume it's active, so I
> would have expected something like:
>
> ret = pcie->cfg->bridge_sw_init_set(pcie, val);
> if (ret)
> pcie->bridge_on = false;
> else
> pcie->bridge_on = !val;
Ack
>
> Tangent: the last "return ret" in brcm_pcie_bridge_sw_init_set_generic()
> should be "return 0" and drop the unnecessary initialization of "ret".
Ack
>
> And the code there would be vastly improved by using FIELD_PREP() or
> u32p_replace_bits() and getting rid of the shifting.
Ack
>
> > + if (pcie->cfg->has_err_report)
> > + spin_unlock_irqrestore(&pcie->bridge_lock, flags);
> > +
> > + return ret;
> > +}
> > +
> > /*
> > * This is to convert the size of the inbound "BAR" region to the
> > * non-linear values of PCIE_X_MISC_RC_BAR[123]_CONFIG_LO.SIZE
> > @@ -1078,7 +1100,7 @@ static int brcm_pcie_setup(struct brcm_pcie *pcie)
> > int memc, ret;
> >
> > /* Reset the bridge */
> > - ret = pcie->cfg->bridge_sw_init_set(pcie, 1);
> > + ret = brcm_pcie_bridge_sw_init_set(pcie, 1);
> > if (ret)
> > return ret;
> >
> > @@ -1094,7 +1116,7 @@ static int brcm_pcie_setup(struct brcm_pcie *pcie)
> > usleep_range(100, 200);
> >
> > /* Take the bridge out of reset */
> > - ret = pcie->cfg->bridge_sw_init_set(pcie, 0);
> > + ret = brcm_pcie_bridge_sw_init_set(pcie, 0);
> > if (ret)
> > return ret;
> >
> > @@ -1545,7 +1567,7 @@ static int brcm_pcie_turn_off(struct brcm_pcie *pcie)
> >
> > if (!(pcie->cfg->quirks & CFG_QUIRK_AVOID_BRIDGE_SHUTDOWN))
> > /* Shutdown PCIe bridge */
> > - ret = pcie->cfg->bridge_sw_init_set(pcie, 1);
> > + ret = brcm_pcie_bridge_sw_init_set(pcie, 1);
> >
> > return ret;
> > }
> > @@ -1633,7 +1655,9 @@ static int brcm_pcie_resume_noirq(struct device *dev)
> > goto err_reset;
> >
> > /* Take bridge out of reset so we can access the SERDES reg */
> > - pcie->cfg->bridge_sw_init_set(pcie, 0);
> > + ret = brcm_pcie_bridge_sw_init_set(pcie, 0);
> > + if (ret)
> > + goto err_reset;
> >
> > /* SERDES_IDDQ = 0 */
> > tmp = readl(base + HARD_DEBUG(pcie));
> > @@ -1901,7 +1925,10 @@ static int brcm_pcie_probe(struct platform_device *pdev)
> > if (ret)
> > return dev_err_probe(&pdev->dev, ret, "could not enable clock\n");
> >
> > - pcie->cfg->bridge_sw_init_set(pcie, 0);
> > + ret = brcm_pcie_bridge_sw_init_set(pcie, 0);
> > + if (ret)
> > + return dev_err_probe(&pdev->dev, ret,
> > + "could not un-reset the bridge\n");
>
> "un-reset" doesn't mean anything to me. Is this the same as "could
> not take the bridge out of reset"? Or maybe "could not deassert
> bridge reset"?
Ack
Thanks,
Jim Quinlan
Broadcom STB/CM
>
> > if (pcie->swinit_reset) {
> > ret = reset_control_assert(pcie->swinit_reset);
> > @@ -1976,6 +2003,9 @@ static int brcm_pcie_probe(struct platform_device *pdev)
> > return ret;
> > }
> >
> > + if (pcie->cfg->has_err_report)
> > + spin_lock_init(&pcie->bridge_lock);
> > +
> > return 0;
> >
> > fail:
> > --
> > 2.34.1
> >
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