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SubjectRe: [patch 2/5] Staging: vme: add VME userspace driver
Emilio G. Cota wrote:
> Martyn Welch wrote:
>
>>>> Instead of using that we implemented a heretic IOCTL-based
>>>> interface for user-space; at least with it you could create a
>>>>
> [ snip ]
>
>>>> #define VME_IOCTL_START_DMA _IOWR('V', 10, struct vme_dma)
>>>>
>>>>
>> I am moving the interface in that direction, I remain unconvinced about
>> the contents of your vme_mapping structure, it's too tsi-148 specific.
>>
>
> Could you please point out why is too tsi148-specific?
>
> The point here is that the driver should know *nothing* about
> windows, etc. What it should just know is:
> - I want a mapping of a certain size to VME address X
>

I'm not convinced. Given that each bridge provides a limited number of
windows (some more than others), we are limited to how large a window we
can produce (we need to map them somewhere) and the potential
combinations are so great (independant 16, 32, 40, 64 and CR/CSR address
spaces, not to mention access modes) it is important to assign the
windows to a driver, so that it may move them as it sees fit. For
example, supporting 10 devices (as you have mentioned earier) with a
single driver could potentially require a single window that it knows it
has exclusive use of to position over each devices register as required
without either having to provide a large window (unfeasibly large on
most/all platforms if they are scattered across the 64-bit address
space) or needing more windows than are available on any of the bridges
I have seen (8 being the maximum).

> The struct provides exactly this.
>
Ah - vme_dma does to some degree. I was talking about vme_mapping for
configuring vme windows, from your vmebus.h:

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* This data structure is used for describing both a hardware window
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* and a logical mapping on top of a hardware window. Therefore some of
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* the fields are only relevant to one of those two entities.
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*/
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struct vme_mapping {
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int window_num;
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/* Reserved for kernel use */
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void *kernel_va;
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/* Reserved for userspace */
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void *user_va;
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int fd;
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/* Window settings */
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int window_enabled;
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enum vme_data_width data_width;
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enum vme_address_modifier am;
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int read_prefetch_enabled;
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enum vme_read_prefetch_size read_prefetch_size;
Tsi-148 specific.

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enum vme_2esst_mode v2esst_mode;
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int bcast_select;
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unsigned int pci_addru;
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unsigned int pci_addrl;
Why are these split, why not a single unsigned long long?

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unsigned int sizeu;
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unsigned int sizel;
Ditto.

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unsigned int vme_addru;
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unsigned int vme_addrl;
Ditto.

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};
In addition your enum vme_address_modifier would need extending when
specifying slave windows, the tsi-148 can support windows with USER and
SUP access, as well as DATA and PRG. Why throw access privileges and
address spaces together like that? The VME spec also specifies 4 User
definable address spaces...

I'm still not convinced by all these structures - you've defined tonnes
of them, I don't feel that it aids readability and maintainability at all.

> Also, could you please send me (off-list) documentation of the
> Universe bridge? It'd be useful for the work on the generic layer.
>
>
It's all over the web :-) We've had it for years and I'm not sure under
what terms we originally got it, so I'm afraid I've got to assume we're
still bound under some NDA, sorry. Searching google for "Universe II
Manual" much get you what you want though...

Martyn

> E.
>



--
Martyn Welch MEng MPhil MIET (Principal Software Engineer) T:+44(0)1327322748
GE Fanuc Intelligent Platforms Ltd, |Registered in England and Wales
Tove Valley Business Park, Towcester, |(3828642) at 100 Barbirolli Square,
Northants, NN12 6PF, UK T:+44(0)1327359444 |Manchester,M2 3AB VAT:GB 927559189

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