linux-kernel - RE: [PATCH v5 0/5] cramfs refresh for embedded usage

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Date:   Fri, 6 Oct 2017 16:07:45 +0000
From:   Chris Brandt <Chris.Brandt@...esas.com>
To:     Christoph Hellwig <hch@...radead.org>,
        Nicolas Pitre <nicolas.pitre@...aro.org>
CC:     Alexander Viro <viro@...iv.linux.org.uk>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-embedded@...r.kernel.org" <linux-embedded@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v5 0/5] cramfs refresh for embedded usage

On Friday, October 06, 2017, Christoph Hellwig wrote:
> This is still missing a proper API for accessing the file system,
> as said before specifying a physical address in the mount command
> line is a an absolute non-no.
> 
> Either work with the mtd folks to get the mtd core down to an absolute
> minimum suitable for you, or figure out a way to specify fs nodes
> through DT or similar.

On my system, the QSPI Flash is memory mapped and set up by the boot 
loader. In order to test the upstream kernel, I use a squashfs image and 
mtd-rom.

So, 0x18000000 is the physical address of flash as it is seen by the 
CPU.

Is there any benefit to doing something similar to this?

	/* File System */
	/* Requires CONFIG_MTD_ROM=y */
	qspi@...00000 {
		compatible = "mtd-rom";
		probe-type = "map_rom";
		reg = <0x18000000 0x4000000>;	/* 64 MB*/
		bank-width = <4>;
		device-width = <1>;

		#address-cells = <1>;
		#size-cells = <1>;

		partition@...000 {
			label ="user";
			reg = <0x0800000 0x800000>; /* 8MB @ 0x18800000 */
			read-only;
		};
	};


Of course this basically ioremaps the entire space on probe, but I think
what you really want to do is just ioremap pages at a time (maybe..I 
might not be following your code correctly)


Chris