linux-kernel - Re: [PATCH 2/3] mfd: lpc_ich: use a correct mask for the GPIO base address

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Date:	Thu, 11 Feb 2016 17:12:38 +0000
From:	Lee Jones <lee.jones@...aro.org>
To:	Peter Tyser <ptyser@...-inc.com>
Cc:	Antoine Tenart <antoine.tenart@...e-electrons.com>,
	linus.walleij@...aro.org, gnurou@...il.com,
	linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
	Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: Re: [PATCH 2/3] mfd: lpc_ich: use a correct mask for the GPIO base
 address

On Mon, 25 Jan 2016, Peter Tyser wrote:

> 
> On Mon, 2016-01-25 at 12:44 +0000, Lee Jones wrote:
> > On Sat, 23 Jan 2016, Antoine Tenart wrote:
> > 
> > > The GPIO base address is read from the GPIOBASE register. The first
> > > bit must be cleared as it can be hardwired to 1 to represent the i/o
> > > space. Other bits are either containing the base address of are
> > > reserved. They should not be cleared as all the chipsets do not have
> > > the same reserved bits.
> > > 
> > > Signed-off-by: Antoine Tenart tenart@...e-electrons.com>
> > > ---
> > >  drivers/mfd/lpc_ich.c | 5 ++++-
> > >  1 file changed, 4 insertions(+), 1 deletion(-)
> > 
> > Applied, thanks.
> 
> Is it possible to hold off on the application of the change Lee?

Patch unapplied.

> > > diff --git a/drivers/mfd/lpc_ich.c b/drivers/mfd/lpc_ich.c
> > > index b514f3cf140d..f13a5ded3958 100644
> > > --- a/drivers/mfd/lpc_ich.c
> > > +++ b/drivers/mfd/lpc_ich.c
> > > @@ -921,7 +921,10 @@ static int lpc_ich_init_gpio(struct pci_dev *dev)
> > >  gpe0_done:
> > >         /* Setup GPIO base register */
> > >         pci_read_config_dword(dev, priv->gbase, &base_addr_cfg);
> > > -       base_addr = base_addr_cfg & 0x0000ff80;
> > > +
> > > +       /* Clear the i/o flag */
> > > +       base_addr = base_addr_cfg & ~BIT(0);
> > > +
> 
> 
> Does this patch work around an issue you are seeing?  Looking at the Bay 
> Trail EDS, the GPIO base address register looks like it should work fine 
> with the original code (it uses 0xff00 as a mask for the address, and 
> reserves 0x80 which reads as a 0).  Also, Bay Trail bit 1 is an enable 
> flag, which this patch wouldn't mask off.  Eg if the BIOS enables the GPIO 
> controller and sets the enable bit, I think things would break with this 
> patch.
> 
> It's also scary to not mask off the reserved bits on other Intel chipsets -
> you're assuming they all read as 0 and I'm not sure if this is true or 
> not.  The patch also doesn't make the same change to the other base 
> register reads either, and ideally they'd be kept in sync.
> 
> Seems like things should be left as-is, or use an accurate chip-specific 
> mask.
> 
> I'd leave as-is personally.  Like Mika mentioned, Baytrail GPIO should 
> already be supported elsewhere, which should make this change unnecessary.
> 
> Regards,
> Peter

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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