linux-kernel - Re: [PATCH 2/2] misc: sram: switch to ioremap

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Message-ID: <20141211103919.GA6067@arm.com>
Date:	Thu, 11 Dec 2014 10:39:20 +0000
From:	Will Deacon <will.deacon@....com>
To:	Philipp Zabel <p.zabel@...gutronix.de>
Cc:	Abhilash Kesavan <a.kesavan@...sung.com>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"heiko@...ech.de" <heiko@...ech.de>,
	"Li.Xiubo@...escale.com" <Li.Xiubo@...escale.com>,
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	"arnd@...db.de" <arnd@...db.de>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
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	"kesavan.abhilash@...il.com" <kesavan.abhilash@...il.com>,
	Pawel Moll <Pawel.Moll@....com>
Subject: Re: [PATCH 2/2] misc: sram: switch to ioremap_wc from ioremap

On Thu, Dec 11, 2014 at 10:08:33AM +0000, Philipp Zabel wrote:
> Hi Abhilash,
> 
> Am Donnerstag, den 11.12.2014, 08:28 +0530 schrieb Abhilash Kesavan:
> > Currently, the SRAM allocator returns device memory via ioremap.
> > This causes issues on ARM64 when the internal SoC SRAM allocated by
> > the generic sram driver is used for audio playback. The destination
> > buffer address (which is ioremapped SRAM) is not 64-bit aligned for
> > certain streams (e.g. 44.1k sampling rate). In such cases we get
> > unhandled alignment faults. Use ioremap_wc in place of ioremap which
> > gives us normal non-cacheable memory instead of device memory.
> 
> Could this break the omap_bus_sync() implementation in
> arch/arm/mach-omap2/omap4-common.c?
> 
>     void omap_bus_sync(void)
>     {
>             if (dram_sync && sram_sync) {
>                     writel_relaxed(readl_relaxed(dram_sync), dram_sync);
>                     writel_relaxed(readl_relaxed(sram_sync), sram_sync);
>                     isb();
>             }
>     }
> 
> It is used in wmb() and omap_do_wfi() to drain interconnect write
> buffers on omap4/5. If sram_sync is mapped with write-combining, could
> the last write to sram_sync stay stuck in the write-combining buffer
> until after the function returns?

I think you have that issue anyway, since you can get an early write
response even if you use ioremap. Does the write to sram_sync have
side-effects that we need to wait for?

Will
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