From mboxrd@z Thu Jan 1 00:00:00 1970 From: gregory.clement@free-electrons.com (Gregory CLEMENT) Date: Thu, 06 Aug 2015 13:14:48 +0200 Subject: [PATCH 7/7] ARM: redo TTBR setup code for LPAE In-Reply-To: <20150805160112.GZ7557@n2100.arm.linux.org.uk> References: <20150506103000.GF2067@n2100.arm.linux.org.uk> <55C22B21.8000700@free-electrons.com> <20150805160112.GZ7557@n2100.arm.linux.org.uk> Message-ID: <55C341A8.5040504@free-electrons.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 05/08/2015 18:01, Russell King - ARM Linux wrote: > On Wed, Aug 05, 2015 at 05:26:25PM +0200, Gregory CLEMENT wrote: >> It seems that since the merge of this commit the secondary CPUs on >> Armada XP failed to come online in Big Endian (my configuration is >> mvebu_v7_defconfig+CONFIG_CPU_BIG_ENDIAN=y). > > That's probably because I don't test big endian at all, never have done, > and I suspect never will as I've never had systems using BE. So, I regard > BE as something of a troublesome untestable burden on kernel development. > (And I've always regarded BE to be an abomination.) In short, I loath > big endian, which really doesn't bode well for me not constantly cocking > it up... > > My guess is that it all comes down to much of the new code expecting the > value in r4/r5 to be the least significant 32bits in r4 and the most > significant 32bits in r5. However, in the secondary code, we load this > using ldrd, which on BE probably reverses that. Thanks for the explanation. > >> Once I found that this commit introduced the regression I also tested >> but with LPAE but I had the same result: only the first CPU boot. > > Not surprising. I guess BE would need the two registers to mcrr reversing > if they were a 64-bit value loaded with ldrd. > > The simple answer may just be to swap r4/r5 after the ldrd. I tried this and it fixed the issue. I will send a patch shortly and if you agree I will submit it to your patch system. Thanks, Gregory -- Gregory Clement, Free Electrons Kernel, drivers, real-time and embedded Linux development, consulting, training and support. http://free-electrons.com