Subject: [PATCH V2] ARM: BCM5301X: Implement SMP support

From: [email-masked] (Jon Mason)
Date: Thu, 22 Oct 2015 16:30:13 -0400

On Wed, Oct 14, 2015 at 08:22:54PM +0200, Hauke Mehrtens wrote:
> On 10/14/2015 03:42 PM, Kapil Hali wrote:
> > 
> > 
> > On 10/14/2015 4:18 AM, Ray Jui wrote:
> >> + bcm-kernel-feedback-list.
> >>
> >> Kapil, you might want to take a look at this. Not sure how this is
> >> related to your SMP patches for NSP.
> > 
> > Ray, I don't have complete/other patch sets for this change. It would
> > be good if I get those patch sets as well or complete e-mail thread. 
> > I think if we have a cleaner solutions for SMP, we can consolidate 
> > the change required for NS and NSP. I have few points to add, which 
> > are inline in this e-mail.
> 
> Hi Kapil,
> 
> the patch was posted on the arm mailing list:
> http://lists.infradead.org/pipermail/linux-arm-kernel/2015-March/332690.html
> but you can also find it in OpenWrt here:
> https://dev.openwrt.org/browser/trunk/target/linux/bcm53xx/patches-4.1/131-ARM-BCM5301X-Implement-SMP-support.patch
> It looks very similar to your approach so I assume we can use the same
> SMP code for NS and NSP. I will look into your patches later on.

Hello Hauke,
With my last patch (https://lkml.org/lkml/2015/10/15/690), SMP on 4708
is working with the NSP SMP patch
(https://lkml.org/lkml/2015/10/14/769).  That patch does not have the
issues that Russell King was mentioning in this patch series (and
supports more SoCs).  Have you had a chance to verify that it works
for you?

Thanks,
Jon

> 
> Hauke
> 
> > 
> >>
> >> On 10/13/2015 3:29 PM, Hauke Mehrtens wrote:
> >>> Hi,
> >>>
> >>> I tested this patch on my device now.
> >>>
> >>> What does the loader do before Linux gets started on the second CPU and
> >>> what is ensured?
> >>>
> >>> On 03/26/2015 01:00 PM, Russell King - ARM Linux wrote:
> >>>> On Sun, Mar 22, 2015 at 02:20:15PM +0100, Rafa? Mi?ecki wrote:
> >>>>> +/*
> >>>>> + * BCM5301X specific entry point for secondary CPUs.
> >>>>> + */
> >>>>> +ENTRY(bcm5301x_secondary_startup)
> >>>>> +	mrc	p15, 0, r0, c0, c0, 5
> >>>>> +	and	r0, r0, #15
> >>>>> +	adr	r4, 1f
> >>>>> +	ldmia	r4, {r5, r6}
> >>>>> +	sub	r4, r4, r5
> >>>>> +	add	r6, r6, r4
> >>>>> +pen:	ldr	r7, [r6]
> >>>>> +	cmp	r7, r0
> >>>>> +	bne	pen
> >>>>> +
> >>>>> +	/*
> >>>>> +	 * In case L1 cache has unpredictable contents at power-up
> >>>>> +	 * clean its contents without flushing.
> >>>>> +	 */
> >>>>> +	bl      v7_invalidate_l1
> >>>>> +
> >>>>> +	mov	r0, #0
> >>>>> +	mcr	p15, 0, r0, c7, c5, 0	/* Invalidate icache */
> >>>>> +	dsb
> >>>>> +	isb
> >>>>
> >>>> So if your I-cache contains unpredictable contents, how do you execute
> >>>> the code to this point?  Shouldn't the I-cache invalidate be the very
> >>>> first instruction you execute followed by the dsb and isb (oh, and iirc
> >>>> it ignores the value in the register).
> >>>>
> >>>> In the case where a CPU has unpredictable contents at power up, the
> >>>> ARM ARM requires that an implementation specific sequence is followed
> >>>> to initialise the caches.  I doubt that such a sequence includes testing
> >>>> a pen value.
> > 
> > Are you sure this is an issue of unpredictable L1 cache contents at
> > power-up? AFAIK, 5301X had an issue with secondary core initialization. 
> > Secondary core which waits on WFE would let it out of the pen as soon as the 
> > first spin_*lock executes. This was because of a BOOTROM bug in NS, so the
> > work around was to reset the address for the secondary processor to go back 
> > and wait for the signal from the primary core. This vector fixup is required
> > so that the secondary core doesn't start executing kernel instructions until 
> > we've patched its jump address during wakeup_secondary().
> > 
> > Also, v7 setup function should invalidate L1 cache and we should remove all
> > v7_invalidate_l1 calls in all headsmp.S in platform specific directories.
> > 
> >>>
> >>> When I remove the test for the pen value the CPU does not come up any
> >>> more, I get this log output:
> >>>
> >>> [ 0.132292] CPU: Testing write buffer coherency: ok
> >>> [ 0.137635] CPU0: thread -1, cpu 0, socket 0, mpidr 80000000
> >>> [ 0.143675] Setting up static identity map for 0x82a0 - 0x82d4
> >>> [ 10.149786] CPU1: failed to boot: -38
> >>> [ 10.153651] Brought up 1 CPUs
> >>>
> >>>
> >>> This was caused just by removing the "cmp r7, r0" and "bne pen"
> >>> instructions.
> >>>
> >>> With these instructions are added it works and I get this:
> >>>
> >>> [    0.132329] CPU: Testing write buffer coherency: ok
> >>> [    0.137682] CPU0: thread -1, cpu 0, socket 0, mpidr 80000000
> >>> [    0.143708] Setting up static identity map for 0x82a0 - 0x82d4
> >>> [    0.189788] CPU1: thread -1, cpu 1, socket 0, mpidr 80000001
> >>> [    0.189892] Brought up 2 CPUs
> >>> [    0.198889] SMP: Total of 2 processors activated (3188.32 BogoMIPS).
> >>>
> >>> Currently this is 100% reproducible.
> >>>
> >>> Could it be that the second CPU needs some time till it is synchronised
> >>> correctly?
> >>>
> >>> I do not know if and why the cache clearing is needed, I do not have
> >>> access to the SoC documentation or the ASIC/firmware developer.
> >>>
> >>>>
> >>>>> +	sysram_base_addr = of_iomap(node, 0);
> >>>>> +	if (!sysram_base_addr) {
> >>>>> +		pr_warn("Failed to map sysram\n");
> >>>>> +		return;
> >>>>> +	}
> >>>>> +
> >>>>> +	writel(virt_to_phys(entry_point), sysram_base_addr + SOC_ROM_LUT_OFF);
> >>>>> +
> >>>>> +	dsb_sev();	/* Exit WFI */
> >>>>
> >>>> Which WFI?  This seems to imply that you have some kind of initial
> >>>> firmware.  If so, that should be taking care of the cache initialisation,
> >>>> not the kernel.
> >>>>
> >>>>> +	mb();		/* make sure write buffer is drained */
> >>>>
> >>>> writel() already ensures that.
> >>>>
> >>>>> +	/*
> >>>>> +	 * The secondary processor is waiting to be released from
> >>>>> +	 * the holding pen - release it, then wait for it to flag
> >>>>> +	 * that it has been released by resetting pen_release.
> >>>>> +	 *
> >>>>> +	 * Note that "pen_release" is the hardware CPU ID, whereas
> >>>>> +	 * "cpu" is Linux's internal ID.
> >>>>> +	 */
> >>>>> +	write_pen_release(cpu_logical_map(cpu));
> >>>>> +
> >>>>> +	 /* Send the secondary CPU SEV */
> >>>>> +	dsb_sev();
> >>>>
> >>>> If you even need any of the pen code, if you're having to send a SEV here,
> >>>> wouldn't having a WFE in the pen assembly loop above be a good idea?
> >>>>
> >>>
> >>>
> >>> I have to read more on how WFE and co works.
> >>>
> >>> Hauke
> >>>
> > 
> > Thanks,
> > Kapil
> > 
>