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Date:   Thu, 7 Jul 2022 11:00:31 -0500
From:   Bjorn Helgaas <helgaas@kernel.org>
To:     Vidya Sagar <vidyas@nvidia.com>
Cc:     jingoohan1@gmail.com, gustavo.pimentel@synopsys.com,
        lpieralisi@kernel.org, robh@kernel.org, kw@linux.com,
        bhelgaas@google.com, linux-pci@vger.kernel.org,
        linux-kernel@vger.kernel.org, kthota@nvidia.com,
        mmaddireddy@nvidia.com, sagar.tv@gmail.com,
        Serge Semin <Sergey.Semin@baikalelectronics.ru>
Subject: Re: [PATCH V1] PCI: designware-ep: Fix DBI access before core init
Message-ID: <20220707160031.GA306375@bhelgaas>
MIME-Version: 1.0
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In-Reply-To: <5c36260c-6bb6-7eb5-be82-c60cd927c02d@nvidia.com>
Precedence: bulk

[+cc Serge]

On Thu, Jul 07, 2022 at 02:39:08PM +0530, Vidya Sagar wrote:
> Hi,
> Anyone has review comments for this change?
> Without this change, Tegra194's endpoint mode is effectively broken.

Did Tegra194 endpoint mode ever work, or has this always been broken.
Wondering if there's a Fixes: or stable tag we should add.  Also cc'd
Serge since he's been doing similar work on dwc.

> On 6/22/2022 9:31 AM, Vidya Sagar wrote:
> > Platforms that cannot support their core initialization without the
> > reference clock from the host, implement the feature 'core_init_notifier'
> > to indicate the DesignWare sub-system about when their core is getting
> > initialized. Any accesses to the core (Ex:- DBI) would result in system
> > hang in such systems (Ex:- tegra194). This patch moves any access to the
> > core to dw_pcie_ep_init_complete() API which is effectively called only
> > after the core initialization.
> > 
> > Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> > ---
> >   .../pci/controller/dwc/pcie-designware-ep.c   | 88 +++++++++++--------
> >   1 file changed, 49 insertions(+), 39 deletions(-)
> > 
> > diff --git a/drivers/pci/controller/dwc/pcie-designware-ep.c b/drivers/pci/controller/dwc/pcie-designware-ep.c
> > index 0eda8236c125..9feec720175f 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware-ep.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware-ep.c
> > @@ -639,9 +639,14 @@ static unsigned int dw_pcie_ep_find_ext_capability(struct dw_pcie *pci, int cap)
> >   int dw_pcie_ep_init_complete(struct dw_pcie_ep *ep)
> >   {
> >   	struct dw_pcie *pci = to_dw_pcie_from_ep(ep);
> > +	struct dw_pcie_ep_func *ep_func;
> > +	struct device *dev = pci->dev;
> > +	struct pci_epc *epc = ep->epc;
> >   	unsigned int offset;
> >   	unsigned int nbars;
> >   	u8 hdr_type;
> > +	u8 func_no;
> > +	void *addr;
> >   	u32 reg;
> >   	int i;
> > @@ -654,6 +659,42 @@ int dw_pcie_ep_init_complete(struct dw_pcie_ep *ep)
> >   		return -EIO;
> >   	}
> > +	dw_pcie_iatu_detect(pci);
> > +
> > +	ep->ib_window_map = devm_kcalloc(dev,
> > +					 BITS_TO_LONGS(pci->num_ib_windows),
> > +					 sizeof(long),
> > +					 GFP_KERNEL);
> > +	if (!ep->ib_window_map)
> > +		return -ENOMEM;
> > +
> > +	ep->ob_window_map = devm_kcalloc(dev,
> > +					 BITS_TO_LONGS(pci->num_ob_windows),
> > +					 sizeof(long),
> > +					 GFP_KERNEL);
> > +	if (!ep->ob_window_map)
> > +		return -ENOMEM;
> > +
> > +	addr = devm_kcalloc(dev, pci->num_ob_windows, sizeof(phys_addr_t),
> > +			    GFP_KERNEL);
> > +	if (!addr)
> > +		return -ENOMEM;
> > +	ep->outbound_addr = addr;
> > +
> > +	for (func_no = 0; func_no < epc->max_functions; func_no++) {
> > +		ep_func = devm_kzalloc(dev, sizeof(*ep_func), GFP_KERNEL);
> > +		if (!ep_func)
> > +			return -ENOMEM;
> > +
> > +		ep_func->func_no = func_no;
> > +		ep_func->msi_cap = dw_pcie_ep_find_capability(ep, func_no,
> > +							      PCI_CAP_ID_MSI);
> > +		ep_func->msix_cap = dw_pcie_ep_find_capability(ep, func_no,
> > +							       PCI_CAP_ID_MSIX);
> > +
> > +		list_add_tail(&ep_func->list, &ep->func_list);
> > +	}
> > +
> >   	offset = dw_pcie_ep_find_ext_capability(pci, PCI_EXT_CAP_ID_REBAR);
> >   	dw_pcie_dbi_ro_wr_en(pci);
> > @@ -677,8 +718,6 @@ EXPORT_SYMBOL_GPL(dw_pcie_ep_init_complete);
> >   int dw_pcie_ep_init(struct dw_pcie_ep *ep)
> >   {
> >   	int ret;
> > -	void *addr;
> > -	u8 func_no;
> >   	struct resource *res;
> >   	struct pci_epc *epc;
> >   	struct dw_pcie *pci = to_dw_pcie_from_ep(ep);
> > @@ -686,7 +725,6 @@ int dw_pcie_ep_init(struct dw_pcie_ep *ep)
> >   	struct platform_device *pdev = to_platform_device(dev);
> >   	struct device_node *np = dev->of_node;
> >   	const struct pci_epc_features *epc_features;
> > -	struct dw_pcie_ep_func *ep_func;
> >   	INIT_LIST_HEAD(&ep->func_list);
> > @@ -708,8 +746,6 @@ int dw_pcie_ep_init(struct dw_pcie_ep *ep)
> >   		}
> >   	}
> > -	dw_pcie_iatu_detect(pci);
> > -
> >   	res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "addr_space");
> >   	if (!res)
> >   		return -EINVAL;
> > @@ -717,26 +753,6 @@ int dw_pcie_ep_init(struct dw_pcie_ep *ep)
> >   	ep->phys_base = res->start;
> >   	ep->addr_size = resource_size(res);
> > -	ep->ib_window_map = devm_kcalloc(dev,
> > -					 BITS_TO_LONGS(pci->num_ib_windows),
> > -					 sizeof(long),
> > -					 GFP_KERNEL);
> > -	if (!ep->ib_window_map)
> > -		return -ENOMEM;
> > -
> > -	ep->ob_window_map = devm_kcalloc(dev,
> > -					 BITS_TO_LONGS(pci->num_ob_windows),
> > -					 sizeof(long),
> > -					 GFP_KERNEL);
> > -	if (!ep->ob_window_map)
> > -		return -ENOMEM;
> > -
> > -	addr = devm_kcalloc(dev, pci->num_ob_windows, sizeof(phys_addr_t),
> > -			    GFP_KERNEL);
> > -	if (!addr)
> > -		return -ENOMEM;
> > -	ep->outbound_addr = addr;
> > -
> >   	if (pci->link_gen < 1)
> >   		pci->link_gen = of_pci_get_max_link_speed(np);
> > @@ -753,20 +769,6 @@ int dw_pcie_ep_init(struct dw_pcie_ep *ep)
> >   	if (ret < 0)
> >   		epc->max_functions = 1;
> > -	for (func_no = 0; func_no < epc->max_functions; func_no++) {
> > -		ep_func = devm_kzalloc(dev, sizeof(*ep_func), GFP_KERNEL);
> > -		if (!ep_func)
> > -			return -ENOMEM;
> > -
> > -		ep_func->func_no = func_no;
> > -		ep_func->msi_cap = dw_pcie_ep_find_capability(ep, func_no,
> > -							      PCI_CAP_ID_MSI);
> > -		ep_func->msix_cap = dw_pcie_ep_find_capability(ep, func_no,
> > -							       PCI_CAP_ID_MSIX);
> > -
> > -		list_add_tail(&ep_func->list, &ep->func_list);
> > -	}
> > -
> >   	if (ep->ops->ep_init)
> >   		ep->ops->ep_init(ep);
> > @@ -790,6 +792,14 @@ int dw_pcie_ep_init(struct dw_pcie_ep *ep)
> >   			return 0;
> >   	}
> > +	/*
> > +	 * NOTE:- Avoid accessing the hardware (Ex:- DBI space) before this
> > +	 * step as platforms that implement 'core_init_notifier' feature may
> > +	 * not have the hardware ready (i.e. core initialized) for access
> > +	 * (Ex: tegra194). Any hardware access on such platforms result
> > +	 * in system hard hang.
> > +	 */
> > +
> >   	return dw_pcie_ep_init_complete(ep);
> >   }
> >   EXPORT_SYMBOL_GPL(dw_pcie_ep_init);
> >