From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from metis.ext.pengutronix.de ([2001:67c:670:201:290:27ff:fe1d:cc33]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kcQBY-00067j-4r for barebox@lists.infradead.org; Tue, 10 Nov 2020 09:43:32 +0000 From: Ahmad Fatoum References: <20201109134430.21156-1-r.czerwinski@pengutronix.de> <20201109134430.21156-3-r.czerwinski@pengutronix.de> <907efaaf5e29ed99229c20ad2398e13b26965827.camel@lynxeye.de> <8df4ad110b83b139381e58bad3e7db82426f9371.camel@pengutronix.de> <20201110074811.GM29830@pengutronix.de> <20201110091543.GP29830@pengutronix.de> <25af706b-3cb1-c7d0-579a-b900ef674692@pengutronix.de> Message-ID: <0e23114b-624f-c789-531f-1d65fd8cbf92@pengutronix.de> Date: Tue, 10 Nov 2020 10:43:30 +0100 MIME-Version: 1.0 In-Reply-To: <25af706b-3cb1-c7d0-579a-b900ef674692@pengutronix.de> Content-Language: en-US List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "barebox" Errors-To: barebox-bounces+u.kleine-koenig=pengutronix.de@lists.infradead.org Subject: Re: [PATCH 2/8] mtd: cfi_flash: allow 0x0 mapping To: Sascha Hauer , Rouven Czerwinski Cc: barebox@lists.infradead.org On 11/10/20 10:36 AM, Ahmad Fatoum wrote: > Hi, > > On 11/10/20 10:15 AM, Sascha Hauer wrote: >> On Tue, Nov 10, 2020 at 08:48:11AM +0100, Sascha Hauer wrote: >>> On Tue, Nov 10, 2020 at 07:33:53AM +0100, Rouven Czerwinski wrote: >>>> On Mon, 2020-11-09 at 14:52 +0100, Lucas Stach wrote: >>>>> Am Montag, den 09.11.2020, 14:44 +0100 schrieb Rouven Czerwinski: >>>>>> Annotate the different read and write functions with >>>>>> zero_page_{access/faulting}. This allows the cfi_flash driver to be used >>>>>> on the QEMU virt machine with an enabled MMU. >>>>> >>>>> I don't like this zero-page access allow in a driver at all. If you >>>>> have some free address space somewhere, you could also solve this issue >>>>> by remapping the IO resource to somewhere else in the address space, >>>>> deviating from the 1:1 mapping. The Tegra PCIe host driver does this, >>>>> if you need some inspiration. >>>> >>>> I totally agree, remapping the IO region sounds like a much better >>>> choice. >>> >>> But where should it be mapped to? Just 4k upwards and hope that the area >>> just above the cfi flash isn't occupied by something else? >> >> Ok, here's the plan: >> >> In a board specific initcall map the memory to wherever it's convenient, >> modify the address of the CFI flash in the device node and add a big >> comment that there's nothing to see here. > > The device tree specification defines a "virtual-reg property [that] specifies > an effective address that maps to the first physical address specified in > the reg property of the device node. This property enables boot programs to > provide client programs with virtual-to-physical mappings that have been set up". > > So, how about a tad more generic approach: > > - barebox device tree extends cfi-flash node with virtual-reg of appropriate > location > - Define a of_iomap() function that Or rather a more generic name, like dev_ioremap?.(In that case !CONFIG_OF is the same as MMU off). > - MMU off => does normal request_iomem_region when MMU is off > - MMU on => remaps reg to virtual-reg and does request_iomem_region > > Advantages: > - No extra board code > - Reusable for others as well > - No device tree patching necessary > > I am not familiar with the PowerPC support in barebox, but if we keep the MMU > on, then the use of virtual-reg is correct and if we turn it off, it doesn't > hurt to have it, so we should be within spec. > > Let me know what you think. > Cheers, > Ahmad > >> >> Sascha >> >> > -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | _______________________________________________ barebox mailing list barebox@lists.infradead.org http://lists.infradead.org/mailman/listinfo/barebox