Re: [linux-usb-devel] [Patch] for UHCI driver (from kernel 2.6.6).

Re: [linux-usb-devel] [Patch] for UHCI driver (from kernel 2.6.6).

[Sven Luther]

On Thu, Jun 17, 2004 at 07:34:54PM +0200, Sven Luther wrote:
> On Mon, Jun 14, 2004 at 08:38:52PM +0100, Alan Cox wrote:
> > On Llu, 2004-06-14 at 16:12, Nicolas DET wrote:
> > > Also, we replace spin_lock_irqxxx/spin_unlock_irq by spin_lock/unlock
> > > (for SMP/PREEMPT kernel) + stop/start_interrupt.
> >
> > This requires a lot of care to do right. Remember that on PC systems
> > interrupts can be substantially posted. A "stop_interrupt" may prevent
> > IRQ issue but if an IRQ is already on the PC APIC bus it will kill you
> > later on because the IRQ delivery and PCI bus access on the PC class
> > machines are totally asynchronous
>
> And what about the other part of the patch ? The one about the
> alignement of the buffer descriptors ? Does it seem sound, should we
> ward it with ppc specific stuff ? Is it fit to be included in the main
> kernel ?

Mmm, it seems that inversing the remove_list and the list also makes the
problem go away, or at least be less important, in :

struct uhci_td {
        /* Hardware fields */
        __u32 link;
        __u32 status;
        __u32 token;
        __u32 buffer;

        /* Software fields */
        dma_addr_t dma_handle;

        struct usb_device *dev;
        struct urb *urb;

        struct list_head list;          /* P: urb->lock */
        struct list_head remove_list;   /* P: uhci->td_remove_list_lock */

        int frame;                      /* for iso: what frame? */
        struct list_head fl_list;       /* P: uhci->frame_list_lock */
} __attribute__((aligned(16)));

Could it be possible that the warning in :

/*
 * The documentation says "4 words for hardware, 4 words for software".
 *
 * That's silly, the hardware doesn't care. The hardware only cares that
 * the hardware words are 16-byte aligned, and we can have any amount of
 * sw space after the TD entry as far as I can tell.

be still important, at least on G4 powerpc ? remove_list is the 5th
software word here. Strange, because supposedly it works on x86 and
other uhci using arches, and it works on the G3, but not on the G4.

Friendly,

Sven Luther

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Re: [linux-usb-devel] [Patch] for UHCI driver (from kernel 2.6.6).

[Benjamin Herrenschmidt]

> be still important, at least on G4 powerpc ? remove_list is the 5th
> software word here. Strange, because supposedly it works on x86 and
> other uhci using arches, and it works on the G3, but not on the G4.

I think it's more likely we are dealing with an ordering issue of
accesses to memory vs. mmio, those aren't order unless you use memory
barriers. Actually, it's worse, you need a full mb() to order them,
which is why lately, we made ppc64 writeX() do full sync's ... that sucks
but it's near to impossible to get an abstract IO API that would cover
our needs here and still make other archs happy it seems...

Ben.


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Re: [linux-usb-devel] [Patch] for UHCI driver (from kernel 2.6.6).

[Alan Stern]

On Fri, 18 Jun 2004, Benjamin Herrenschmidt wrote:

> I think it's more likely we are dealing with an ordering issue of
> accesses to memory vs. mmio, those aren't order unless you use memory
> barriers. Actually, it's worse, you need a full mb() to order them,
> which is why lately, we made ppc64 writeX() do full sync's ... that sucks
> but it's near to impossible to get an abstract IO API that would cover
> our needs here and still make other archs happy it seems...

I recently changed a few mb() calls to wmb(), because they only protected
data the CPU was writing to be read by the device.  Do you think changing
all the wmb()'s back to mb()'s would make a difference?

(Actually it seems likely that this is _not_ directly related to the
original problem, but it might be important anyway.)

Alan Stern


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Re: [linux-usb-devel] [Patch] for UHCI driver (from kernel 2.6.6).

[Benjamin Herrenschmidt]

On Fri, 2004-06-18 at 16:41, Alan Stern wrote:
> On Fri, 18 Jun 2004, Benjamin Herrenschmidt wrote:
>
> > I think it's more likely we are dealing with an ordering issue of
> > accesses to memory vs. mmio, those aren't order unless you use memory
> > barriers. Actually, it's worse, you need a full mb() to order them,
> > which is why lately, we made ppc64 writeX() do full sync's ... that sucks
> > but it's near to impossible to get an abstract IO API that would cover
> > our needs here and still make other archs happy it seems...
>
> I recently changed a few mb() calls to wmb(), because they only protected
> data the CPU was writing to be read by the device.  Do you think changing
> all the wmb()'s back to mb()'s would make a difference?
>
> (Actually it seems likely that this is _not_ directly related to the
> original problem, but it might be important anyway.)

Well, the problem on ppc is that the eieio done by wmb() (or implicitely
done by all writeX IO accessors) will only order stores in the same
domain. That is cacheable aren't ordered vs. non cacheables.

For example, write to a descriptor in memory, then writel() to your
device, that isn't guaranteed to happen in order.

In this case, you indeed need an mb(), but that's a ppc thing and the
race on ppc32 CPUs is quite small (though ppc64, typically POWER4 and
POWER5, will eat you for lunch with their multiple deep store queues).

Ben


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Re: [linux-usb-devel] [Patch] for UHCI driver (from kernel 2.6.6).

[Oliver Neukum]

Am Freitag, 18. Juni 2004 23:41 schrieb Alan Stern:
> > barriers. Actually, it's worse, you need a full mb() to order them,
> > which is why lately, we made ppc64 writeX() do full sync's ... that sucks
> > but it's near to impossible to get an abstract IO API that would cover
> > our needs here and still make other archs happy it seems...
>
> I recently changed a few mb() calls to wmb(), because they only protected
> data the CPU was writing to be read by the device.  Do you think changing
> all the wmb()'s back to mb()'s would make a difference?

Are these issues documented somewhere?

	Regards
		Oliver

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Re: [linux-usb-devel] [Patch] for UHCI driver (from kernel 2.6.6).

[Alan Stern]

On Fri, 18 Jun 2004, Benjamin Herrenschmidt wrote:

> > I recently changed a few mb() calls to wmb(), because they only protected
> > data the CPU was writing to be read by the device.  Do you think changing
> > all the wmb()'s back to mb()'s would make a difference?
> >
> > (Actually it seems likely that this is _not_ directly related to the
> > original problem, but it might be important anyway.)
>
> Well, the problem on ppc is that the eieio done by wmb() (or implicitely
> done by all writeX IO accessors) will only order stores in the same
> domain. That is cacheable aren't ordered vs. non cacheables.

I'm not familiar with the term "eieio"; can you explain it?

> For example, write to a descriptor in memory, then writel() to your
> device, that isn't guaranteed to happen in order.

Then it shouldn't matter for what I'm doing, which involves multiple
writes to the same region of "consistent" memory.  Or maybe it's only
"coherent" memory -- the important thing is that the first write must
complete and be visible to the device's DMA before the second.  wmb()
will suffice for that, right?

> In this case, you indeed need an mb(), but that's a ppc thing and the
> race on ppc32 CPUs is quite small (though ppc64, typically POWER4 and
> POWER5, will eat you for lunch with their multiple deep store queues).

Thanks,

Alan Stern


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Re: [linux-usb-devel] [Patch] for UHCI driver (from kernel 2.6.6).

[Sven Luther]

On Sat, Jun 19, 2004 at 09:59:53AM -0400, Alan Stern wrote:
> On Fri, 18 Jun 2004, Benjamin Herrenschmidt wrote:
>
> > > I recently changed a few mb() calls to wmb(), because they only protected
> > > data the CPU was writing to be read by the device.  Do you think changing
> > > all the wmb()'s back to mb()'s would make a difference?
> > >
> > > (Actually it seems likely that this is _not_ directly related to the
> > > original problem, but it might be important anyway.)
> >
> > Well, the problem on ppc is that the eieio done by wmb() (or implicitely
> > done by all writeX IO accessors) will only order stores in the same
> > domain. That is cacheable aren't ordered vs. non cacheables.
>
> I'm not familiar with the term "eieio"; can you explain it?

Enforced In-Order Execution of I/O. Page 8-61 of the Programing
Environments for 32-Bit Microprocessors, by motorola, well, at least on
my version.

Friendly,

Sven Luther

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Re: [linux-usb-devel] [Patch] for UHCI driver (from kernel 2.6.6).

[Segher Boessenkool]

> Enforced In-Order Execution of I/O. Page 8-61 of the Programing
> Environments for 32-Bit Microprocessors, by motorola, well, at least on
> my version.

Don't use that old stuff; use either the new PEM or the Book I/II/III:

PEM (64- and 32-bit) v2.0:
http://www-3.ibm.com/chips/techlib/techlib.nsf/techdocs/
F6153E213FDD912E87256D49006C6541/$file/pem._64bit.d20030611.pdf

PowerPC Book I/II/III v2.01:
www-106.ibm.com/developerworks/eserver/pdfs/archpub1.pdf
www-106.ibm.com/developerworks/eserver/pdfs/archpub2.pdf
www-106.ibm.com/developerworks/eserver/pdfs/archpub3.pdf

Most of the time the Books are better; sometimes the PEM helps
as well.

Have fun,


Segher


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Re: [linux-usb-devel] [Patch] for UHCI driver (from kernel 2.6.6).

[Sven Luther]

On Mon, Jun 21, 2004 at 10:18:40AM +0200, Segher Boessenkool wrote:
> >Enforced In-Order Execution of I/O. Page 8-61 of the Programing
> >Environments for 32-Bit Microprocessors, by motorola, well, at least on
> >my version.
>
> Don't use that old stuff; use either the new PEM or the Book I/II/III:

Well, the nice thing about the old stuff like you said, is that i got it
in nice paper book format, and not a bunch of .pdfs, which Motorola used
to ship for free back in the days. But sure, i will look at those new
documents.

> PEM (64- and 32-bit) v2.0:
> http://www-3.ibm.com/chips/techlib/techlib.nsf/techdocs/
> F6153E213FDD912E87256D49006C6541/$file/pem._64bit.d20030611.pdf
>
> PowerPC Book I/II/III v2.01:
> www-106.ibm.com/developerworks/eserver/pdfs/archpub1.pdf
> www-106.ibm.com/developerworks/eserver/pdfs/archpub2.pdf
> www-106.ibm.com/developerworks/eserver/pdfs/archpub3.pdf
>
> Most of the time the Books are better; sometimes the PEM helps
> as well.

Friendly,

Sven Luther

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