Re: [PATCH][3/4] usb: ohci-sm501 driver

["Magnus Damm" <magnus.damm@xxxxxxxxx>]

On Jan 15, 2008 4:54 PM, David Brownell <david-b@xxxxxxxxxxx> wrote:
> On Sunday 13 January 2008, Magnus Damm wrote:
> > usb: ohci-sm501 driver
> >
> > This patch adds sm501 ohci support.
>
> Just sm501, not the sm502 you had mentioned?

The driver works with sm502 as well. sm501 and sm502 seem very
similar. The sm502 device is using the same pci device id as sm501.
The sm501 mfd driver works well with sm502 devices - at least for my
little setup.

> > It's all very straightforward with the
> > exception of dma_declare_coherent_memory() and HCD_BOUNCE.
>
> If I skimmed those docs right, sm502 won't always need that.
>
> For example, if the sm502 is hooked up through PCI, it doesn't
> necessarily even need to have local memory ... or use it for
> OHCI, if it's present.  (Certainly there's a DMA controller
> on the chip that can do PCI bus mastering.  I'm assuming that
> the OHCI silicon is hooked up to that controller...)

You may be right. I'm not sure if it can do PCI bus mastering and if
the ohci block is hooked up to the dma controller. I have not played
around so much with the PCI interface.

My main goal is to add support for usb to some embedded boards made by
Renesas. They are hooked up with "slave mode" so they need the bounce
buffers. And the bounce buffers _do_ work for pci as well - I just
double checked using my sm502 pci card.

> If that's so, that stuff should be a function of how the
> platform device was configured.  For example, an sm502 on
> a PCI card might set up a bunch of platform devices for
> its various functions (assuming they don't show up as normal
> functions) ... but without memory resource #1, thereby
> signaling that it doesn't need to use local memory or
> do the dma_alloc_coherent() dance.

I totally agree. I can probably allocate find time to hack up pci bus
mastering support - if it works properly that is. Given that, would it
be possible to accept this implementation as a first step? It does
work for both "slave mode" and pci, even if pci may be suboptimal. I
prefer to see pci bus mastering as an enhancement.

/ magnus

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