From mboxrd@z Thu Jan 1 00:00:00 1970 From: York Sun Subject: Re: Need some guidance on i2c-ocores driver Date: Mon, 20 Apr 2015 11:31:39 -0700 Message-ID: <5535460B.2060309@freescale.com> References: <55304D8E.8070204@freescale.com> <55312AF7.7070504@freescale.com> <20150420064231.GE3447@x1> <55352839.70905@freescale.com> <20150420181651.GF3447@x1> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20150420181651.GF3447@x1> Sender: linux-kernel-owner@vger.kernel.org To: Lee Jones Cc: Julia.Lawall@lip6.fr, linux-i2c@vger.kernel.org, wolfram@the-dreams.de, linux-kernel@vger.kernel.org List-Id: linux-i2c@vger.kernel.org On 04/20/2015 11:16 AM, Lee Jones wrote: > On Mon, 20 Apr 2015, York Sun wrote: > >> >> >> On 04/19/2015 11:42 PM, Lee Jones wrote: >>> On Fri, 17 Apr 2015, York Sun wrote: >>> >>>> Resend to LKML >>>> >>>> Lee, >>>> >>>> This question is actually more about MFD. Can you point me to the possible >>>> causes for my failure below? >>> >>> It's hard to tell exactly without code, but it looks like you're >>> trying to allocate overlapping memory regions. Double check all of >>> your addresses. For DT you need to take a look at your 'reg' >>> properties, for traditional platform data it's best to grep for >>> IORESOURCE_MEM. >>> >> Lee, >> >> It _is_ overlapping. How could it not be? The resource for the I2C is mapped to >> BAR2. So the resource is overlapping with BAR2. It is alway the case, isn't it? >> What I don't understand is how MFD works with the resources if it is guaranteed >> overlapping. Did I get something wrong? >> >> Look at the reference code I took, drivers/mfd/timberdale.c, when >> 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. York