Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1357537

[PATCH 4.4 15/50] dmaengine: at_xdmac: fix residue computation

From Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Newsgroups linux.kernel
Subject [PATCH 4.4 15/50] dmaengine: at_xdmac: fix residue computation
Date 2016-03-14 19:30 +0100
Message-ID <rcFpD-7uk-1@gated-at.bofh.it> (permalink)
References <rcEWC-73F-7@gated-at.bofh.it>
Organization linux.* mail to news gateway

Show all headers | View raw

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

------------------

From: Ludovic Desroches <ludovic.desroches@atmel.com>

commit 25c5e9626ca4d40928dc9c44f009ce2ed0a739e7 upstream.

When computing the residue we need two pieces of information: the current
descriptor and the remaining data of the current descriptor. To get
that information, we need to read consecutively two registers but we
can't do it in an atomic way. For that reason, we have to check manually
that current descriptor has not changed.

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Suggested-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>
Reported-by: David Engraf <david.engraf@sysgo.com>
Tested-by: David Engraf <david.engraf@sysgo.com>
Fixes: e1f7c9eee707 ("dmaengine: at_xdmac: creation of the atmel
eXtended DMA Controller driver")
Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/dma/at_xdmac.c |   42 +++++++++++++++++++++++++++++++++++++++---
 1 file changed, 39 insertions(+), 3 deletions(-)

--- a/drivers/dma/at_xdmac.c
+++ b/drivers/dma/at_xdmac.c
@@ -176,6 +176,7 @@
 #define AT_XDMAC_MAX_CHAN	0x20
 #define AT_XDMAC_MAX_CSIZE	16	/* 16 data */
 #define AT_XDMAC_MAX_DWIDTH	8	/* 64 bits */
+#define AT_XDMAC_RESIDUE_MAX_RETRIES	5
 
 #define AT_XDMAC_DMA_BUSWIDTHS\
 	(BIT(DMA_SLAVE_BUSWIDTH_UNDEFINED) |\
@@ -1383,8 +1384,8 @@ at_xdmac_tx_status(struct dma_chan *chan
 	struct at_xdmac_desc	*desc, *_desc;
 	struct list_head	*descs_list;
 	enum dma_status		ret;
-	int			residue;
-	u32			cur_nda, mask, value;
+	int			residue, retry;
+	u32			cur_nda, check_nda, cur_ubc, mask, value;
 	u8			dwidth = 0;
 	unsigned long		flags;
 
@@ -1421,7 +1422,42 @@ at_xdmac_tx_status(struct dma_chan *chan
 			cpu_relax();
 	}
 
+	/*
+	 * When processing the residue, we need to read two registers but we
+	 * can't do it in an atomic way. AT_XDMAC_CNDA is used to find where
+	 * we stand in the descriptor list and AT_XDMAC_CUBC is used
+	 * to know how many data are remaining for the current descriptor.
+	 * Since the dma channel is not paused to not loose data, between the
+	 * AT_XDMAC_CNDA and AT_XDMAC_CUBC read, we may have change of
+	 * descriptor.
+	 * For that reason, after reading AT_XDMAC_CUBC, we check if we are
+	 * still using the same descriptor by reading a second time
+	 * AT_XDMAC_CNDA. If AT_XDMAC_CNDA has changed, it means we have to
+	 * read again AT_XDMAC_CUBC.
+	 * Memory barriers are used to ensure the read order of the registers.
+	 * A max number of retries is set because unlikely it can never ends if
+	 * we are transferring a lot of data with small buffers.
+	 */
 	cur_nda = at_xdmac_chan_read(atchan, AT_XDMAC_CNDA) & 0xfffffffc;
+	rmb();
+	cur_ubc = at_xdmac_chan_read(atchan, AT_XDMAC_CUBC);
+	for (retry = 0; retry < AT_XDMAC_RESIDUE_MAX_RETRIES; retry++) {
+		rmb();
+		check_nda = at_xdmac_chan_read(atchan, AT_XDMAC_CNDA) & 0xfffffffc;
+
+		if (likely(cur_nda == check_nda))
+			break;
+
+		cur_nda = check_nda;
+		rmb();
+		cur_ubc = at_xdmac_chan_read(atchan, AT_XDMAC_CUBC);
+	}
+
+	if (unlikely(retry >= AT_XDMAC_RESIDUE_MAX_RETRIES)) {
+		ret = DMA_ERROR;
+		goto spin_unlock;
+	}
+
 	/*
 	 * Remove size of all microblocks already transferred and the current
 	 * one. Then add the remaining size to transfer of the current
@@ -1434,7 +1470,7 @@ at_xdmac_tx_status(struct dma_chan *chan
 		if ((desc->lld.mbr_nda & 0xfffffffc) == cur_nda)
 			break;
 	}
-	residue += at_xdmac_chan_read(atchan, AT_XDMAC_CUBC) << dwidth;
+	residue += cur_ubc << dwidth;
 
 	dma_set_residue(txstate, residue);

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH 4.4 00/50] 4.4.6-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:10 +0100
  [PATCH 4.4 11/50] KVM: MMU: fix reserved bit check for ept=0/CR0.WP=0/CR4.SMEP=1/EFER.NX=0 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:10 +0100
  [PATCH 4.4 47/50] MIPS: smp.c: Fix uninitialised temp_foreign_map Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:10 +0100
  [PATCH 4.4 10/50] KVM: MMU: fix ept=0/pte.u=1/pte.w=0/CR0.WP=0/CR4.SMEP=1/EFER.NX=0 combo Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:10 +0100
  [PATCH 4.4 14/50] tracing: Fix check for cpu online when event is disabled Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:10 +0100
  [PATCH 4.4 39/50] Revert "drm/radeon/pm: adjust display configuration after powerstate" Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 30/50] mac80211: minstrel_ht: set default tx aggregation timeout to 0 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 21/50] ASoC: wm8958: Fix enum ctl accesses in a wrong type Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 27/50] iwlwifi: mvm: inc pending frames counter also when txing non-sta Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 43/50] userfaultfd: dont block on the last VM updates at exit time Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 32/50] mac80211: check PN correctly for GCMP-encrypted fragmented MPDUs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 26/50] can: gs_usb: fixed disconnect bug by removing erroneous use of kfree() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 40/50] powerpc: Fix dedotify for binutils >= 2.26 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 28/50] mac80211: minstrel: Change expected throughput unit back to Kbps Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 33/50] mac80211: Fix Public Action frame RX in AP mode Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 41/50] powerpc/powernv: Add a kmsg_dumper that flushes console output on panic Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 29/50] mac80211: fix use of uninitialised values in RX aggregation Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 22/50] ovl: ignore lower entries when checking purity of non-directory entries Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 04/50] ARM: OMAP2+: hwmod: Introduce ti,no-idle dt property Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 45/50] ovl: fix getcwd() failure after unsuccessful rmdir Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 23/50] ovl: fix working on distributed fs as lower layer Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 03/50] ARM: dts: dra7: do not gate cpsw clock due to errata i877 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 02/50] ARM: mvebu: fix overlap of Crypto SRAM with PCIe memory window Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 24/50] wext: fix message delay/ordering Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 06/50] kvm: cap halt polling at exactly halt_poll_ns Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 44/50] ovl: copy new uid/gid into overlayfs runtime inode Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 35/50] x86/mm: Fix slow_virt_to_phys() for X86_PAE again Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 42/50] powerpc/powernv: Fix OPAL_CONSOLE_FLUSH prototype and usages Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 34/50] gpu: ipu-v3: Do not bail out on missing optional port nodes Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 15/50] dmaengine: at_xdmac: fix residue computation Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:30 +0100
  [PATCH 4.4 25/50] cfg80211/wext: fix message ordering Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:30 +0100
  [PATCH 4.4 20/50] ASoC: wm8994: Fix enum ctl accesses in a wrong type Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:30 +0100
  [PATCH 4.4 19/50] ASoC: samsung: Use IRQ safe spin lock calls Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:30 +0100
  Re: [PATCH 4.4 00/50] 4.4.6-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2016-03-15 00:20 +0100
    Re: [PATCH 4.4 00/50] 4.4.6-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-16 16:50 +0100
  Re: [PATCH 4.4 00/50] 4.4.6-stable review Guenter Roeck <linux@roeck-us.net> - 2016-03-15 03:40 +0100
    Re: [PATCH 4.4 00/50] 4.4.6-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-16 16:50 +0100

csiph-web