From: Vineet Gupta <Vineet.Gupta1@synopsys.com>
To: Will Deacon <will.deacon@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"arnd@arndb.de" <arnd@arndb.de>,
"arc-linux-dev@synopsys.com" <arc-linux-dev@synopsys.com>
Subject: Re: [PATCH 20/28] ARCv2: barriers
Date: Tue, 23 Jun 2015 13:32:17 +0530 [thread overview]
Message-ID: <55891289.5070909@synopsys.com> (raw)
In-Reply-To: <20150622133656.GG1583@arm.com>
On Monday 22 June 2015 07:06 PM, Will Deacon wrote:
>> OK, so given that regular/mmio is also weakly ordered, it would seem that we need
>> > full mb() *before* and *after* the IO access in the non relaxed API. ARM code
>> > seems to put a rmb() after the readl and wmb() before the writel. Is that based on
>> > how h/w provides for some ?
> We figured that you'd likely be doing something like:
>
> <writel_relaxed DMA buffer>
> <writel MMIO "go" reg>
>
> or:
>
> <readl MMIO "status" reg>
> <readl_relaxed DMA buffer>
>
> so ended up with writel doing {wmb(); writel_relaxed} and readl doing
> {readl_relaxed; rmb()}.
>
>> > In one of the links you posted above, Catalin posed the same question, but I
>> > didn't see response to that.
>> >
>> > | If we are to make the writel/readl on ARM fully ordered with both IO
>> > | (enforced by hardware) and uncached memory, do we add barriers on each
>> > | side of the writel/readl etc.? The common cases would require a barrier
>> > | before writel (write buffer flushing) and a barrier after readl (in case
>> > | of polling for a "DMA complete" state).
>> > |
>> > | So if io_wmb() just orders to IO writes (writel_relaxed), does it mean
>> > | that we still need a mighty wmb() that orders any type of accesses (i.e.
>> > | uncached memory vs IO)? Can drivers not use the strict writel() and no
>> > | longer rely on wmb() (wondering whether we could simplify it on ARM with
>> > | fully ordered IO accessors)?
>> >
>> > Further readl/writel would be no different than ioread32/iowrite32 ?
> ioread32/iowrite32 can be used with port addresses and dispatch to the
> relevant accessors depending on that. The memory ordering semantics should
> be the same as readl/writel.
>
>> > FWIW, h/w folks tell me that DMB guarentess local barrier semantics so we don't
>> > need to use DSYNC. Latter only provides full r+w+TLB/BPU stuff while DMB allows
>> > finer grained r/w/r+w. But if we need full mb then using one vs. other becomes a
>> > moot point.
> I'd say go with what we do on ARM/arm64, then at least we have consistency
> in the use of barriers.
Thx for very helpful review/feedback Will. I've posted a v2 !
-Vineet
next prev parent reply other threads:[~2015-06-23 8:02 UTC|newest]
Thread overview: 109+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-09 11:48 [PATCH 00/28] ARCv2 port to Linux - (B) ISA / Core / platform support Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 11:48 ` [PATCH 01/28] ARCv2: [intc] HS38 core interrupt controller Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 11:48 ` [PATCH 02/28] ARCv2: Support for ARCv2 ISA and HS38x cores Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 11:48 ` [PATCH 03/28] ARCv2: STAR 9000793984: Handle return from intr to Delay Slot Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 11:48 ` [PATCH 04/28] ARCv2: STAR 9000808988: signals involving " Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 11:48 ` [PATCH 05/28] ARCv2: STAR 9000814690: Really Re-enable interrupts to avoid deadlocks Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 11:48 ` [PATCH 06/28] ARCv2: MMUv4: TLB programming Model changes Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 11:48 ` [PATCH 07/28] ARCv2: MMUv4: cache programming model changes Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 11:48 ` [PATCH 08/28] ARCv2: MMUv4: support aliasing icache config Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 11:48 ` [PATCH 09/28] ARCv2: optimised string/mem lib routines Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 11:48 ` [PATCH 10/28] ARCv2: Adhere to Zero Delay loop restriction Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 11:48 ` [PATCH 11/28] ARCv2: extable: Enable sorting at build time Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-24 5:51 ` Vineet Gupta
2015-06-24 5:51 ` Vineet Gupta
2015-06-29 20:38 ` David Daney
2015-06-30 4:41 ` Vineet Gupta
2015-06-30 4:41 ` Vineet Gupta
2015-06-09 11:48 ` [PATCH 12/28] ARCv2: clocksource: Introduce 64bit local RTC counter Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 11:48 ` [PATCH 13/28] ARC: make plat_smp_ops weak to allow over-rides Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 11:48 ` [PATCH 14/28] ARCv2: SMP: ARConnect debug/robustness Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 11:48 ` [PATCH 15/28] ARCv2: SMP: clocksource: Enable Global Real Time counter Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 11:48 ` [PATCH 16/28] ARCv2: SMP: intc: IDU 2nd level intc for dynamic IRQ distribution Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 11:48 ` [PATCH 17/28] ARC: add compiler barrier to LLSC based cmpxchg Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 12:23 ` Peter Zijlstra
2015-06-09 11:48 ` [PATCH 18/28] ARC: add smp barriers around atomics per memory-barrriers.txt Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 12:30 ` Peter Zijlstra
2015-06-10 9:17 ` Vineet Gupta
2015-06-10 10:53 ` Peter Zijlstra
2015-06-11 13:03 ` Vineet Gupta
2015-06-12 12:15 ` [PATCH v2] ARC: add smp barriers around atomics per Documentation/atomic_ops.txt Vineet Gupta
2015-06-12 12:15 ` Vineet Gupta
2015-06-12 13:04 ` Peter Zijlstra
2015-06-12 13:16 ` Vineet Gupta
2015-06-09 11:48 ` [PATCH 19/28] arch: conditionally define smp_{mb,rmb,wmb} Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 12:32 ` Peter Zijlstra
2015-06-09 11:48 ` [PATCH 20/28] ARCv2: barriers Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 12:40 ` Peter Zijlstra
2015-06-10 9:34 ` Vineet Gupta
2015-06-10 10:58 ` Peter Zijlstra
2015-06-10 13:01 ` Will Deacon
2015-06-11 12:13 ` Vineet Gupta
2015-06-11 13:39 ` Will Deacon
2015-06-19 13:13 ` Vineet Gupta
2015-06-19 13:13 ` Vineet Gupta
2015-06-19 13:13 ` Vineet Gupta
2015-06-22 13:36 ` Will Deacon
2015-06-22 13:36 ` Will Deacon
2015-06-22 13:36 ` Will Deacon
2015-06-23 7:58 ` [PATCH v2 " Vineet Gupta
2015-06-23 7:58 ` Vineet Gupta
2015-06-23 8:49 ` Will Deacon
2015-06-23 9:03 ` Vineet Gupta
2015-06-23 9:26 ` Will Deacon
2015-06-23 9:52 ` [PATCH v3 22/28] " Vineet Gupta
2015-06-23 9:52 ` Vineet Gupta
2015-06-23 16:28 ` Will Deacon
2015-06-23 9:25 ` [PATCH v2 20/28] " Peter Zijlstra
2015-06-23 8:02 ` Vineet Gupta [this message]
2015-06-09 11:48 ` [PATCH 21/28] ARC: Reduce bitops lines of code using macros Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-12 12:20 ` [PATCH v2] " Vineet Gupta
2015-06-12 12:20 ` Vineet Gupta
2015-06-12 13:05 ` Peter Zijlstra
2015-06-09 11:48 ` [PATCH 22/28] ARCv2: STAR 9000837815 workaround hardware exclusive transactions livelock Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 12:35 ` Peter Zijlstra
2015-06-10 10:01 ` Vineet Gupta
2015-06-10 11:02 ` Peter Zijlstra
2015-06-19 9:55 ` [PATCH v2 " Vineet Gupta
2015-06-19 9:55 ` Vineet Gupta
2015-06-19 9:59 ` Will Deacon
2015-06-19 10:09 ` Vineet Gupta
2015-06-23 7:59 ` Vineet Gupta
2015-06-23 7:59 ` Vineet Gupta
2015-06-09 11:48 ` [PATCH 23/28] ARCv2: SLC: Handle explcit flush for DMA ops (w/o IO-coherency) Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 11:48 ` [PATCH 24/28] ARCv2: All bits in place, allow ARCv2 builds Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 11:48 ` [PATCH 25/28] ARCv2: [nsim*hs*] Support simulation platforms for HS38x cores Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 11:48 ` [PATCH 26/28] ARC: [axs101] Prepare for AXS103 Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 11:48 ` [PATCH 27/28] ARCv2: [axs103] Support ARC SDP FPGA platform for HS38x cores Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
2015-06-09 11:48 ` [PATCH 28/28] ARCv2: [vdk] dts files and defconfig for HS38 VDK Vineet Gupta
2015-06-09 11:48 ` Vineet Gupta
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