linux-kernel - Re: [RFC PATCH 1/3] PCI: iproc: generate proper configuration access cycles

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Date:	Tue, 27 Oct 2015 10:18:20 +0800
From:	Jisheng Zhang <jszhang@...vell.com>
To:	Ray Jui <rjui@...adcom.com>
CC:	<bhelgaas@...gle.com>, <thierry.reding@...il.com>,
	<swarren@...dotorg.org>, <gnurou@...il.com>, <tinamdar@....com>,
	<sbranden@...adcom.com>, <linux@....linux.org.uk>,
	<linux-tegra@...r.kernel.org>, <linux-pci@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<bcm-kernel-feedback-list@...adcom.com>
Subject: Re: [RFC PATCH 1/3] PCI: iproc: generate proper configuration
 access cycles

On Mon, 26 Oct 2015 10:18:14 -0700
Ray Jui <rjui@...adcom.com> wrote:

> Hi Jisheng,
> 
> On 10/26/2015 4:02 AM, Jisheng Zhang wrote:
> > Inspired by Russell King's patch[1], I found current iproc also has the
> > same issue of "reading 32-bits from the command register, modifying the
> > command register, and then writing it back has the effect of clearing
> > any status bits that were indicating at that time" as pointed out by
> > Russell. This patch fix this issue by using the pci_generic_config_write.
> >
> > [1]http://www.spinics.net/lists/linux-pci/msg44869.html
> >
> > Signed-off-by: Jisheng Zhang <jszhang@...vell.com>
> > ---
> >   drivers/pci/host/pcie-iproc.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/pci/host/pcie-iproc.c b/drivers/pci/host/pcie-iproc.c
> > index fe2efb1..0c423f2 100644
> > --- a/drivers/pci/host/pcie-iproc.c
> > +++ b/drivers/pci/host/pcie-iproc.c
> > @@ -111,7 +111,7 @@ static void __iomem *iproc_pcie_map_cfg_bus(struct pci_bus *bus,
> >   static struct pci_ops iproc_pcie_ops = {
> >   	.map_bus = iproc_pcie_map_cfg_bus,
> >   	.read = pci_generic_config_read32,
> > -	.write = pci_generic_config_write32,
> > +	.write = pci_generic_config_write,
> >   };
> >
> >   static void iproc_pcie_reset(struct iproc_pcie *pcie)
> >  
> 
> I have already confirmed with the ASIC team that the current iProc PCIe 
> controller requires 32-bit aligned access into the configuration space 
> due to the way how it was integrated into various iProc SoCs including 
> NSP, Cygnus, and NS2.
> 
> This change will prevent the driver from working properly.
> 
> I've informed our ASIC team about this issue and all future iProc based 
> SoCs should be able to support 8-bit, 16-bit access and therefore 
> pci_generic_config_write/read can be used for those SoCs.
> 
> Thanks,
> 
> Ray

Got it. 

Thanks for the information,
Jisheng
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