From: Alan Stern <stern@rowland.harvard.edu>
To: Mark Salter <msalter@redhat.com>
Cc: ming.lei@canonical.com, greg@kroah.com,
linux-usb@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
linux-omap@vger.kernel.org, Russell King <linux@arm.linux.org.uk>
Subject: Re: [PATCH] usb: ehci: make HC see up-to-date qh/qtd descriptor ASAP
Date: Tue, 30 Aug 2011 13:15:42 -0400 (EDT) [thread overview]
Message-ID: <Pine.LNX.4.44L0.1108301312020.2109-100000@iolanthe.rowland.org> (raw)
In-Reply-To: <1314722311.2344.64.camel@deneb.redhat.com>
On Tue, 30 Aug 2011, Mark Salter wrote:
> On Wed, 2011-08-31 at 00:03 +0800, ming.lei@canonical.com wrote:
> > +/*
> > + * Writing to dma coherent memory on ARM may be delayed via L2
> > + * writing buffer, so introduce the helper which can flush L2 writing
> > + * buffer into memory immediately, especially used to flush ehci
> > + * descriptor to memory.
> > + * */
> > +#ifdef CONFIG_ARM_DMA_MEM_BUFFERABLE
> > +static inline void ehci_sync_mem()
> > +{
> > + mb();
> > +}
> > +#else
> > +static inline void ehci_sync_mem()
> > +{
> > +}
> > +#endif
> > +
>
> I'm wondering if this doesn't really belong in the DMA API for any
> future architectures that can't avoid prolonged write buffering to DMA
> coherent memory. IIUC, ARM mitigates this for most drivers by including
> an implicit write buffer flush in the mmio write routines. This takes
> care of the drivers which write to a mmio device register after writing
> something to shared DMA memory. IIUC, this doesn't help ehci because the
> host controller is polling to see what the cpu writes to the shared
> memory. Other hardware which polls shared memory like that will likely
> have the same problem and could use buffer drain helpers as well.
This would be a good thing to define centrally. Would you like to
post an RFC on LKML?
Do you know of any other examples of hardware that polls shared DMA
memory?
Alan Stern
WARNING: multiple messages have this Message-ID (diff)
From: stern@rowland.harvard.edu (Alan Stern)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] usb: ehci: make HC see up-to-date qh/qtd descriptor ASAP
Date: Tue, 30 Aug 2011 13:15:42 -0400 (EDT) [thread overview]
Message-ID: <Pine.LNX.4.44L0.1108301312020.2109-100000@iolanthe.rowland.org> (raw)
In-Reply-To: <1314722311.2344.64.camel@deneb.redhat.com>
On Tue, 30 Aug 2011, Mark Salter wrote:
> On Wed, 2011-08-31 at 00:03 +0800, ming.lei at canonical.com wrote:
> > +/*
> > + * Writing to dma coherent memory on ARM may be delayed via L2
> > + * writing buffer, so introduce the helper which can flush L2 writing
> > + * buffer into memory immediately, especially used to flush ehci
> > + * descriptor to memory.
> > + * */
> > +#ifdef CONFIG_ARM_DMA_MEM_BUFFERABLE
> > +static inline void ehci_sync_mem()
> > +{
> > + mb();
> > +}
> > +#else
> > +static inline void ehci_sync_mem()
> > +{
> > +}
> > +#endif
> > +
>
> I'm wondering if this doesn't really belong in the DMA API for any
> future architectures that can't avoid prolonged write buffering to DMA
> coherent memory. IIUC, ARM mitigates this for most drivers by including
> an implicit write buffer flush in the mmio write routines. This takes
> care of the drivers which write to a mmio device register after writing
> something to shared DMA memory. IIUC, this doesn't help ehci because the
> host controller is polling to see what the cpu writes to the shared
> memory. Other hardware which polls shared memory like that will likely
> have the same problem and could use buffer drain helpers as well.
This would be a good thing to define centrally. Would you like to
post an RFC on LKML?
Do you know of any other examples of hardware that polls shared DMA
memory?
Alan Stern
next prev parent reply other threads:[~2011-08-30 17:15 UTC|newest]
Thread overview: 65+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-08-30 16:03 [PATCH] usb: ehci: make HC see up-to-date qh/qtd descriptor ASAP ming.lei-Z7WLFzj8eWMS+FvcfC7Uqw
2011-08-30 16:03 ` ming.lei at canonical.com
2011-08-30 16:15 ` Alan Stern
2011-08-30 16:15 ` Alan Stern
2011-08-30 16:38 ` Mark Salter
2011-08-30 16:38 ` Mark Salter
2011-08-30 17:15 ` Alan Stern [this message]
2011-08-30 17:15 ` Alan Stern
2011-08-30 18:45 ` Mark Salter
2011-08-30 18:45 ` Mark Salter
2011-08-30 17:26 ` Will Deacon
2011-08-30 17:26 ` Will Deacon
[not found] ` <20110830172642.GE3464-SGELLbQ0bobZROr8t4l/smS4ubULX0JqMm0uRHvK7Nw@public.gmane.org>
2011-08-30 17:48 ` Greg KH
2011-08-30 17:48 ` Greg KH
2011-08-30 17:54 ` Will Deacon
2011-08-30 17:54 ` Will Deacon
[not found] ` <20110830175432.GG3464-SGELLbQ0bobZROr8t4l/smS4ubULX0JqMm0uRHvK7Nw@public.gmane.org>
2011-08-31 0:23 ` Chen Peter-B29397
2011-08-31 0:23 ` Chen Peter-B29397
2011-08-31 8:49 ` Will Deacon
2011-08-31 8:49 ` Will Deacon
2011-08-31 12:33 ` Chen Peter-B29397
2011-08-31 12:33 ` Chen Peter-B29397
2011-08-31 13:43 ` Mark Salter
2011-08-31 13:43 ` Mark Salter
2011-08-31 15:21 ` Will Deacon
2011-08-31 15:21 ` Will Deacon
2011-08-31 15:27 ` Mark Salter
2011-08-31 15:27 ` Mark Salter
2011-08-31 16:12 ` Marc Zyngier
2011-08-31 16:12 ` Marc Zyngier
2011-08-31 16:55 ` Marc Dietrich
2011-08-31 16:55 ` Marc Dietrich
2011-09-01 10:34 ` Marc Zyngier
2011-09-01 10:34 ` Marc Zyngier
[not found] ` <4E5F5FA9.3010305-5wv7dgnIgG8@public.gmane.org>
2011-09-01 11:13 ` Marc Dietich
2011-09-01 11:13 ` Marc Dietich
2011-09-01 19:08 ` Stephen Warren
2011-09-01 19:08 ` Stephen Warren
2011-09-02 9:50 ` Marc Zyngier
2011-09-02 9:50 ` Marc Zyngier
2011-09-02 17:07 ` Stephen Warren
2011-09-02 17:07 ` Stephen Warren
[not found] ` <74CDBE0F657A3D45AFBB94109FB122FF04B327A383-C7FfzLzN0UxDw2glCA4ptUEOCMrvLtNR@public.gmane.org>
2011-09-02 11:13 ` Marc Dietich
2011-09-02 11:13 ` Marc Dietich
2011-08-31 17:46 ` Nicolas Pitre
2011-08-31 17:46 ` Nicolas Pitre
2011-08-31 17:51 ` Will Deacon
2011-08-31 17:51 ` Will Deacon
[not found] ` <20110831175147.GI8777-SGELLbQ0bobZROr8t4l/smS4ubULX0JqMm0uRHvK7Nw@public.gmane.org>
2011-08-31 18:19 ` Rob Herring
2011-08-31 18:19 ` Rob Herring
2011-08-31 18:35 ` Mark Salter
2011-08-31 18:35 ` Mark Salter
2011-08-31 18:49 ` Rob Herring
2011-08-31 18:49 ` Rob Herring
[not found] ` <4E5E8230.9060307-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2011-08-31 18:58 ` Mark Salter
2011-08-31 18:58 ` Mark Salter
2011-08-31 19:35 ` Will Deacon
2011-08-31 19:35 ` Will Deacon
2011-09-08 22:41 ` Mark Salter
2011-09-08 22:41 ` Mark Salter
[not found] ` <1315521779.2313.29.camel-PDpCo7skNiwAicBL8TP8PQ@public.gmane.org>
2011-10-31 6:49 ` Pandita, Vikram
2011-10-31 6:49 ` Pandita, Vikram
2011-08-31 0:56 ` Ming Lei
2011-08-31 0:56 ` Ming Lei
2011-09-01 23:16 ` Grant Grundler
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