linux-kernel - Re: Need some guidance on i2c-ocores driver

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Message-ID: <20150421073534.GK3447@x1>
Date:	Tue, 21 Apr 2015 08:35:34 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	York Sun <yorksun@...escale.com>
Cc:	Julia.Lawall@...6.fr, linux-i2c@...r.kernel.org,
	wolfram@...-dreams.de, linux-kernel@...r.kernel.org
Subject: Re: Need some guidance on i2c-ocores driver

> >> mfd_add_devices() is called, it uses &dev->resource as the base. So the BAR will
> >> be the parent. Check the code in mfd-core.c, mfd_add_device(),
> >>
> >> if ((cell->resources[r].flags & IORESOURCE_MEM) && mem_base) {
> >> 	res[r].parent = mem_base;
> >> 	res[r].start = mem_base->start + cell->resources[r].start;
> >> 	res[r].end = mem_base->start + cell->resources[r].end;
> >> }
> >>
> >> So the MFD resource is within its parent. When later the device driver request a
> >> region, will it get conflict with the parent?
> > 
> > I doubt you'll want to map the same memory area in both the parent and
> > the child device drivers.  Only map the registers you plan to use in
> > the driver you plan to use them.  If you need multiple devices to
> > access the same registers then you need to create an API, complete
> > with locking, in the MFD parent device.
> 
> Thanks for pointing out. I thought at first the conflict was due to my
> pci_ioremap_bar(). I went ahead to remove the mapping but still not working.
> Your email inspired me to take a deeper look at my code and I found my error. I
> have called pci_request_regions() which reserves all BARs. I think that's my
> root cause. Thanks for helping me.

You are welcome.

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