[PATCH V2] ARM: BCM5301X: Implement SMP support

[Russell King - ARM Linux]

On Sun, Mar 22, 2015 at 02:20:15PM +0100, Rafał Miłecki 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.

> +	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?

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