Re: [PATCH 1/2] PCI: brcmstb: Add a way to indicate if PCIe bridge is active

[Bjorn Helgaas <helgaas@kernel.org>]

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@broadcom.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;

Tangent: the last "return ret" in brcm_pcie_bridge_sw_init_set_generic()
should be "return 0" and drop the unnecessary initialization of "ret".

And the code there would be vastly improved by using FIELD_PREP() or
u32p_replace_bits() and getting rid of the shifting.

> +	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"?

>  	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
>