[PATCH] arm: Improve MMC performance on Versatile Express

[Pawel Moll]

VE suffers from serious problem with MMC transfers - low performance,
errors when other IO peripherals (especially USB) are used at the
same time etc.

It all boils down to the MMC controller short FIFO and - in result -
timing constrains. The most problematic case - USB driver hogging
CPU and MMC FIFO under/overruns in the result - can be mitigated on
SMP system by distributing interrupts handling for these peripherals
between cores.

With this, the MMC card clock can be safely (at least it looks like
it) increased to 1.5MHz, improving performance.

Signed-off-by: Pawel Moll <pawel.moll at arm.com>
---
 arch/arm/mach-vexpress/v2m.c |   14 ++++++++++++++
 1 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/arch/arm/mach-vexpress/v2m.c b/arch/arm/mach-vexpress/v2m.c
index 4b5af01..300ac72 100644
--- a/arch/arm/mach-vexpress/v2m.c
+++ b/arch/arm/mach-vexpress/v2m.c
@@ -244,6 +244,7 @@ static unsigned int v2m_mmci_status(struct device *dev)
 static struct mmci_platform_data v2m_mmci_data = {
 	.ocr_mask	= MMC_VDD_32_33|MMC_VDD_33_34,
 	.status		= v2m_mmci_status,
+	.f_max		= 1500000,
 };
 
 static AMBA_DEVICE(aaci,  "mb:aaci",  V2M_AACI, NULL);
@@ -391,6 +392,19 @@ static void __init v2m_init(void)
 	for (i = 0; i < ARRAY_SIZE(v2m_amba_devs); i++)
 		amba_device_register(v2m_amba_devs[i], &iomem_resource);
 
+	/* WARNING: HACK HACK HACK!
+	 *
+	 * MMCI cell has very tight timing requirements regarding interrupt
+	 * handling (fractions of millisecond), while the USB host controller
+	 * interrupt handler can hog the CPU for more then 1 millisecond!
+	 *
+	 * To mitigate the problem on SMP systems, we can set CPU affinities
+	 * of these interrupts to different cores... */
+	BUG_ON(v2m_usb_resources[1].flags != IORESOURCE_IRQ);
+	irq_set_affinity(v2m_usb_resources[1].start, cpumask_of(0));
+	irq_set_affinity(mmci_device.irq[0], cpumask_of(1));
+	irq_set_affinity(mmci_device.irq[1], cpumask_of(1));
+
 	pm_power_off = v2m_power_off;
 	arm_pm_restart = v2m_restart;
 
-- 
1.6.3.3