linux-kernel - Re: [PATCH] PCI: dwc: Warn only for non-prefetchable memory resource size >4GB

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Message-ID: <20200518155435.GA2299@e121166-lin.cambridge.arm.com>
Date:   Mon, 18 May 2020 16:54:35 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Vidya Sagar <vidyas@...dia.com>, jingoohan1@...il.com,
        gustavo.pimentel@...opsys.com,
        Andrew Murray <amurray@...goodpenguin.co.uk>,
        bhelgaas@...gle.com, thierry.reding@...il.com,
        jonathanh@...dia.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, kthota@...dia.com,
        mmaddireddy@...dia.com, sagar.tv@...il.com,
        Alan Mikhak <alan.mikhak@...ive.com>
Subject: Re: [PATCH] PCI: dwc: Warn only for non-prefetchable memory resource
 size >4GB

On Wed, May 13, 2020 at 05:35:08PM -0500, Bjorn Helgaas wrote:
> [+cc Alan; please cc authors of relevant commits,
> updated Andrew's email address]
> 
> On Thu, May 14, 2020 at 12:38:55AM +0530, Vidya Sagar wrote:
> > commit 9e73fa02aa009 ("PCI: dwc: Warn if MEM resource size exceeds max for
> > 32-bits") enables warning for MEM resources of size >4GB but prefetchable
> >  memory resources also come under this category where sizes can go beyond
> > 4GB. Avoid logging a warning for prefetchable memory resources.
> > 
> > Signed-off-by: Vidya Sagar <vidyas@...dia.com>
> > ---
> >  drivers/pci/controller/dwc/pcie-designware-host.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> > index 42fbfe2a1b8f..a29396529ea4 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> > @@ -366,7 +366,8 @@ int dw_pcie_host_init(struct pcie_port *pp)
> >  			pp->mem = win->res;
> >  			pp->mem->name = "MEM";
> >  			mem_size = resource_size(pp->mem);
> > -			if (upper_32_bits(mem_size))
> > +			if (upper_32_bits(mem_size) &&
> > +			    !(win->res->flags & IORESOURCE_PREFETCH))
> >  				dev_warn(dev, "MEM resource size exceeds max for 32 bits\n");
> >  			pp->mem_size = mem_size;
> >  			pp->mem_bus_addr = pp->mem->start - win->offset;

That warning was added for a reason - why should not we log legitimate
warnings ? AFAIU having resources larger than 4GB can lead to undefined
behaviour given the current ATU programming API.

Alan ? I want to understand what's the best course of action before
merging these patches.

Lorenzo