From mboxrd@z Thu Jan 1 00:00:00 1970 From: jason@lakedaemon.net (Jason Cooper) Date: Tue, 16 Dec 2014 07:22:24 -0500 Subject: How much flash space should I reserve for device tree blobs? In-Reply-To: References: Message-ID: <20141216122224.GG967@titan.lakedaemon.net> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hey Brian, +Arnd, Olof. On Mon, Dec 15, 2014 at 03:33:50PM -0500, Brian Hutchinson wrote: > Reflecting back on the famous quote of "Nobody needs more than 640K", > how much space should I reserve in flash to 'future proof' my MTD map > in regards to dtb's? > > Looking at the current flavors of dtb's built in a recent mainline > kernel, the biggest one I see is 66K. > > How big do you all see these getting? I know, it's probably a loaded > question. Would just like to bounce this off the list as a sanity > check ... measure twice cut once kind of thing. There's probably better folks to answer this than me (former powerpc folks, eg Arnd, Olof), but since I've had to consider it as well, I'll tell you my thoughts. The biggest unknown is the addition of binary blobs. If those are a consideration for your board(s), then you need to reserve quite a bit more space. For example, a binding update could start including the firmware for an SD wifi card. However, in the interest of retaining backwards compatibility, Linux would still be able to load from /lib/firmware. So, if you couldn't update your dtb, you'd still have a working wifi card. If you aren't concerned about binary blobs, then I'd say you're fine with 128k or so. Most of the scenarios I had were with 2MB NOR flash. barebox is usually in the range of 200k, and there isn't enough room left for the kernel, so I had plenty for the environment and the dtb. hth, Jason.