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

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Message-ID: <1418298046.3188.10.camel@pengutronix.de>
Date:	Thu, 11 Dec 2014 12:40:46 +0100
From:	Philipp Zabel <p.zabel@...gutronix.de>
To:	Will Deacon <will.deacon@....com>
Cc:	Abhilash Kesavan <a.kesavan@...sung.com>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Tony Lindgren <tony@...mide.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"heiko@...ech.de" <heiko@...ech.de>,
	"Li.Xiubo@...escale.com" <Li.Xiubo@...escale.com>,
	"shc_work@...l.ru" <shc_work@...l.ru>,
	"nicoleotsuka@...il.com" <nicoleotsuka@...il.com>,
	"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>,
	"corbet@....net" <corbet@....net>,
	"padma.v@...sung.com" <padma.v@...sung.com>,
	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	"shawn.guo@...escale.com" <shawn.guo@...escale.com>,
	"bcousson@...libre.com" <bcousson@...libre.com>,
	"tony@...mide.com" <tony@...mide.com>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>,
	"kgene@...nel.org" <kgene@...nel.org>,
	"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

Hi Will,

Am Donnerstag, den 11.12.2014, 10:39 +0000 schrieb Will Deacon:
> 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?

[Added Tony Lindgren and Santosh Shilimkar to Cc:]
I don't know.

regards
Philipp

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