linux-kernel - [PATCH 4.2.y-ckt 32/93] dmaengine: hsu: correct use of channel status register

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Message-Id: <1461694653-29506-33-git-send-email-kamal@canonical.com>
Date:	Tue, 26 Apr 2016 11:16:32 -0700
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Vinod Koul <vinod.koul@...el.com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 4.2.y-ckt 32/93] dmaengine: hsu: correct use of channel status register

4.2.8-ckt9 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

commit 4f4bc0abff79dc9d7ccbd3143adbf8ad1f4fe6ab upstream.

There is a typo in documentation regarding to descriptor empty bit (DESCE)
which is set to 1 when descriptor is empty. Thus, status register at the end of
a transfer usually returns all DESCE bits set and thus it will never be zero.

Moreover, there are 2 bits (CDESC) that encode current descriptor, on which
interrupt has been asserted. In case when we have few descriptors programmed we
might have non-zero value.

Remove DESCE and CDESC bits from DMA channel status register (HSU_CH_SR) when
reading it.

Fixes: 2b49e0c56741 ("dmaengine: append hsu DMA driver")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Signed-off-by: Vinod Koul <vinod.koul@...el.com>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 drivers/dma/hsu/hsu.c | 2 +-
 drivers/dma/hsu/hsu.h | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/dma/hsu/hsu.c b/drivers/dma/hsu/hsu.c
index f42f71e..b863b68 100644
--- a/drivers/dma/hsu/hsu.c
+++ b/drivers/dma/hsu/hsu.c
@@ -143,7 +143,7 @@ static u32 hsu_dma_chan_get_sr(struct hsu_dma_chan *hsuc)
 	sr = hsu_chan_readl(hsuc, HSU_CH_SR);
 	spin_unlock_irqrestore(&hsuc->lock, flags);
 
-	return sr;
+	return sr & ~(HSU_CH_SR_DESCE_ANY | HSU_CH_SR_CDESC_ANY);
 }
 
 irqreturn_t hsu_dma_irq(struct hsu_dma_chip *chip, unsigned short nr)
diff --git a/drivers/dma/hsu/hsu.h b/drivers/dma/hsu/hsu.h
index 0275233..6a54f35 100644
--- a/drivers/dma/hsu/hsu.h
+++ b/drivers/dma/hsu/hsu.h
@@ -41,6 +41,9 @@
 #define HSU_CH_SR_DESCTO(x)	BIT(8 + (x))
 #define HSU_CH_SR_DESCTO_ANY	(BIT(11) | BIT(10) | BIT(9) | BIT(8))
 #define HSU_CH_SR_CHE		BIT(15)
+#define HSU_CH_SR_DESCE(x)	BIT(16 + (x))
+#define HSU_CH_SR_DESCE_ANY	(BIT(19) | BIT(18) | BIT(17) | BIT(16))
+#define HSU_CH_SR_CDESC_ANY	(BIT(31) | BIT(30))
 
 /* Bits in HSU_CH_CR */
 #define HSU_CH_CR_CHA		BIT(0)
-- 
2.7.4