From mboxrd@z Thu Jan 1 00:00:00 1970 From: Simon Horman Date: Fri, 06 Jun 2014 06:25:23 +0000 Subject: Re: [PATCH] ARM: shmobile: Lager memory map update Message-Id: <20140606062518.GA13049@verge.net.au> List-Id: References: <20140605060601.12351.26135.sendpatchset@w520> In-Reply-To: <20140605060601.12351.26135.sendpatchset@w520> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-sh@vger.kernel.org On Fri, Jun 06, 2014 at 06:24:07AM +0900, Magnus Damm wrote: > Hi Geert, > > On Thu, Jun 5, 2014 at 5:17 PM, Geert Uytterhoeven wrote: > > Hi Magnus, > > > > On Thu, Jun 5, 2014 at 8:06 AM, Magnus Damm wrote: > >> From: Magnus Damm > >> > >> Update the Lager DTS to make use of the new unified legacy > >> memory map where the legacy window on Lager and Koelsch > >> have the same size. > >> > >> After update the Lager board has the following map: > >> Bank0: 1GiB RAM (Legacy 32-bit: 0x40000000->0x7fffffff) > >> Bank1: 3GiB RAM (LPAE area: 0x140000000->0x1ffffffff) > >> > >> Before the update the old map looked like this: > >> Bank0: 2GiB RAM (Legacy 32-bit: 0x40000000->0xbfffffff) > >> Bank1: 2GiB RAM (LPAE area: 0x180000000->0x1ffffffff) > >> > >> Tested with and without LPAE on r8a7790 Lager. > >> > >> Signed-off-by: Magnus Damm > > > > I think this lacks an explanation why you want this... > > The reason is that the legacy portion of the memory map (what is > included in the 32-bit space) should be unified between Lager and > Koelsch. I've been asked to do this, and I suspect it is related to > simplify u-boot board support. It is not however 100% clear to me. Now > the memory map will at least match documentation. I think it would be best if some reason was included in the changelog. I am willing to accept "align code with documentation" at a minimum. But something more verbose may aid us when looking over this again in the future. > > > In general, less highmem is better ;-) > > Well, yes, that I agree to. But in this particular case with the > common 3G/1G user/kernel virtual memory split the amount of highmem > actually remains the same. =) From highmem/lowmem perspective this > patch simply takes 1GiB of highmem from the legacy window and moves it > into the LPAE area that also is accessed as highmem. LPAE needs to be > enabled to get all the memory though, but that was needed before > anyway. So this patch really makes no big difference when 3G/1G is > used. > > However for other split mode like 2G/2G the amount of potential lowmem > is reduced. It is however my understanding that this split mode is > however incompatible with the USB Host controllers. Also, on Lager > regardless how you adjust your split mode you need to enable LPAE to > get access to all memory. > > Cheers, > > / magnus >