Patch "stmmac: Discard masked flags in interrupt status register" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

stmmac: Discard masked flags in interrupt status register

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
stmmac-discard-masked-flags-in-interrupt-status-register.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Alexey Brodkin <[email protected]>
Date: Fri, 27 Jan 2017 15:24:43 +0300
Subject: stmmac: Discard masked flags in interrupt status register

From: Alexey Brodkin <[email protected]>

[ Upstream commit 0a764db103376cf69d04449b10688f3516cc0b88 ]

DW GMAC databook says the following about bits in "Register 15 (Interrupt Mask Register)":
--------------------------->8-------------------------
When set, this bit __disables_the_assertion_of_the_interrupt_signal__ because of the setting of XXX bit in Register 14 (Interrupt Status Register). --------------------------->8-------------------------

In fact even if we mask one bit in the mask register it doesn't prevent corresponding bit to appear in the status register, it only disables interrupt generation for corresponding event.

But currently we expect a bit different behavior: status bits to be in sync with their masks, i.e. if mask for bit A is set in the mask register then bit A won't appear in the interrupt status register.

This was proven to be incorrect assumption, see discussion here [1]. That misunderstanding causes unexpected behaviour of the GMAC, for example we were happy enough to just see bogus messages about link state changes.

So from now on we'll be only checking bits that really may trigger an interrupt.

[1] https://lkml.org/lkml/2016/11/3/413

---
 drivers/net/ethernet/stmicro/stmmac/dwmac1000_core.c |    4 ++++
 1 file changed, 4 insertions(+)

@@ -305,8 +305,12 @@ static int dwmac1000_irq_status(struct m
 {
 	void __iomem *ioaddr = hw->pcsr;
 	u32 intr_status = readl(ioaddr + GMAC_INT_STATUS);
+	u32 intr_mask = readl(ioaddr + GMAC_INT_MASK);
 	int ret = 0;
 
+	/* Discard masked bits */
+	intr_status &= ~intr_mask;
+
 	/* Not used events (e.g. MMC interrupts) are not handled. */
 	if ((intr_status & GMAC_INT_STATUS_MMCTIS))
 		x->mmc_tx_irq_n++;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/stmmac-discard-masked-flags-in-interrupt-status-register.patch