linux-kernel - Re: [PATCH 3/5] PCI: st: Provide support for the sti PCIe controller

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Date:	Wed, 21 Jan 2015 20:35:41 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Gabriel Fernandez <gabriel.fernandez@...aro.org>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Gabriel FERNANDEZ <gabriel.fernandez@...com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Srinivas Kandagatla <srinivas.kandagatla@...il.com>,
	Maxime Coquelin <maxime.coquelin@...com>,
	Patrice Chotard <patrice.chotard@...com>,
	Russell King <linux@....linux.org.uk>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Mohit Kumar <mohit.kumar@...com>,
	Jingoo Han <jg1.han@...sung.com>,
	Grant Likely <grant.likely@...aro.org>,
	Fabrice Gasnier <fabrice.gasnier@...com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Thierry Reding <treding@...dia.com>,
	Minghuan Lian <Minghuan.Lian@...escale.com>,
	Magnus Damm <damm@...nsource.se>,
	Will Deacon <will.deacon@....com>,
	Tanmay Inamdar <tinamdar@....com>,
	Murali Karicheri <m-karicheri2@...com>,
	Kishon Vijay Abraham I <kishon@...com>,
	Pratyush Anand <pratyush.anand@...com>,
	Sachin Kamat <sachin.kamat@...sung.com>,
	Andrew Lunn <andrew@...n.ch>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Srikanth Thokala <sthokal@...inx.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"kernel@...inux.com" <kernel@...inux.com>,
	linux-pci@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Lee Jones <lee.jones@...aro.org>
Subject: Re: [PATCH 3/5] PCI: st: Provide support for the sti PCIe controller

On Wednesday 21 January 2015 16:47:36 Gabriel Fernandez wrote:
> On 19 January 2015 at 14:49, Arnd Bergmann <arnd@...db.de> wrote:
> > On Monday 19 January 2015 13:37:33 Gabriel Fernandez wrote:
> >> On 17 December 2014 at 23:14, Arnd Bergmann <arnd@...db.de> wrote:
> >> > On Wednesday 17 December 2014 11:34:44 Gabriel FERNANDEZ wrote:
> >> > > +/*
> >> > > + * On ARM platforms, we actually get a bus error returned when the PCIe
> >> > IP
> >> > > + * returns a UR or CRS instead of an OK.
> >> > > + */
> >> > > +static int st_pcie_abort_
> >> >
> >> > handler(unsigned long addr, unsigned int fsr,
> >> > > +                              struct pt_regs *regs)
> >> > > +{
> >> > > +     return 0;
> >> > > +}
> >> >
> >> > You should check that it's actually PCI that caused the abort. Don't
> >> > just ignore a hard error condition.
> >> >
> >> > Usually there are registers in the PCI core that let you identify what
> >> > happened.
> >> >
> >>
> >>
> >> We return 0 because abort handler is not activated during boot.
> >>
> >
> > Can you just remove the handler then? We should never have exception
> > handlers that unconditionally return 0.
> >
> 
> Ah sorry, we need the handler because we can received aborts from
> user-land after the boot.
> 
> I have 2 solutions, the first to simplify we can only return 0.
> The second is to manage handler during boot. Then i need for that a
> new patch from Fabrice
> https://lkml.org/lkml/2014/2/7/631

I still don't get it. What is causing the abort? Is that something
user space does, or is it just a condition that gets stuck the pcie
device after probing that gets delivered once as soon as the aborts
are enabled?

> >>
> >> msi_data is a virtual address, it's obtained through a   __get_free_pages()
> >> function in dw_pcie_msi_init() procedure.
> >
> > I guess you need dma_map_single() then, or use dma_alloc_coherent instead
> > of __get_free_pages(). There is no guarantee that the page you allocate
> > there is actually visible to the PCI host at the same address that the CPU
> > uses, so you need to map from a CPU address to a DMA address that the PCI
> > host bridge uses.
> >
> >         Arnd
> 
> This is only to check the msi magic address given to ip, we never read
> or write in this area.
> this code is only a check

But doesn't the hardware access the pointer?

	Arnd
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