mtd: bcm47xxsflash: use uncached MMIO access for BCM53573

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Gitweb:     http://git.infradead.org/?p=mtd-2.6.git;a=commit;h=64ad46379fcf14f437553f654d1adcd3d0e0d7f9
Commit:     64ad46379fcf14f437553f654d1adcd3d0e0d7f9
Parent:     0e2ce9d3fcba5f92dd6c2b27d82690e49d0c0854
Author:     Rafał Miłecki <rafal at milecki.pl>
AuthorDate: Mon Aug 15 14:21:28 2016 +0200
Committer:  Brian Norris <computersforpeace at gmail.com>
CommitDate: Mon Nov 7 18:17:37 2016 -0800

    mtd: bcm47xxsflash: use uncached MMIO access for BCM53573
    
    BCM53573 is a new series of Broadcom's SoCs. It's based on ARM and uses
    this old ChipCommon-based flash access. Early tests resulted in flash
    corruptions that were tracked down to using cached MMIO for flash read
    access. Switch to ioremap_nocache conditionally to support BCM53573 and
    don't break performance on old MIPS devices.
    
    Signed-off-by: Rafał Miłecki <rafal at milecki.pl>
    Reviewed-by: Boris Brezillon <boris.brezillon at free-electrons.com>
    Signed-off-by: Brian Norris <computersforpeace at gmail.com>
---
 drivers/mtd/devices/bcm47xxsflash.c | 24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/drivers/mtd/devices/bcm47xxsflash.c b/drivers/mtd/devices/bcm47xxsflash.c
index 1c65c15..514be04 100644
--- a/drivers/mtd/devices/bcm47xxsflash.c
+++ b/drivers/mtd/devices/bcm47xxsflash.c
@@ -296,16 +296,30 @@ static int bcm47xxsflash_bcma_probe(struct platform_device *pdev)
 		dev_err(dev, "can't request region for resource %pR\n", res);
 		return -EBUSY;
 	}
-	b47s->window = ioremap_cache(res->start, resource_size(res));
-	if (!b47s->window) {
-		dev_err(dev, "ioremap failed for resource %pR\n", res);
-		return -ENOMEM;
-	}
 
 	b47s->bcma_cc = container_of(sflash, struct bcma_drv_cc, sflash);
 	b47s->cc_read = bcm47xxsflash_bcma_cc_read;
 	b47s->cc_write = bcm47xxsflash_bcma_cc_write;
 
+	/*
+	 * On old MIPS devices cache was magically invalidated when needed,
+	 * allowing us to use cached access and gain some performance. Trying
+	 * the same on ARM based BCM53573 results in flash corruptions, we need
+	 * to use uncached access for it.
+	 *
+	 * It may be arch specific, but right now there is only 1 ARM SoC using
+	 * this driver, so let's follow Broadcom's reference code and check
+	 * ChipCommon revision.
+	 */
+	if (b47s->bcma_cc->core->id.rev == 54)
+		b47s->window = ioremap_nocache(res->start, resource_size(res));
+	else
+		b47s->window = ioremap_cache(res->start, resource_size(res));
+	if (!b47s->window) {
+		dev_err(dev, "ioremap failed for resource %pR\n", res);
+		return -ENOMEM;
+	}
+
 	switch (b47s->bcma_cc->capabilities & BCMA_CC_CAP_FLASHT) {
 	case BCMA_CC_FLASHT_STSER:
 		b47s->type = BCM47XXSFLASH_TYPE_ST;