Hi
Am 28.09.20 um 08:50 schrieb Christian König:
> Am 27.09.20 um 21:16 schrieb Sam Ravnborg:
>> Hi Thomas.
>>
>>>> struct simap {
>>>> union {
>>>> void __iomem *vaddr_iomem;
>>>> void *vaddr;
>>>> };
>>>> bool is_iomem;
>>>> };
>>>>
>>>> Where simap is a shorthand for system_iomem_map
>>>> And it could al be stuffed into a include/linux/simap.h file.
>>>>
>>>> Not totally sold on the simap name - but wanted to come up with
>>>> something.
>>> Yes. Others, myself included, have suggested to use a name that does not
>>> imply a connection to the dma-buf framework, but no one has come up with
>>> a good name.
>>>
>>> I strongly dislike simap, as it's entirely non-obvious what it does.
>>> dma-buf-map is not actually wrong. The structures represents the mapping
>>> of a dma-able buffer in most cases.
>>>
>>>> With this approach users do not have to pull in dma-buf to use it and
>>>> users will not confuse that this is only for dma-buf usage.
>>> There's no need to enable dma-buf. It's all in the header file without
>>> dependencies on dma-buf. It's really just the name.
>>>
>>> But there's something else to take into account. The whole issue here is
>>> that the buffer is disconnected from its originating driver, so we don't
>>> know which kind of memory ops we have to use. Thinking about it, I
>>> realized that no one else seemed to have this problem until now.
>>> Otherwise there would be a solution already. So maybe the dma-buf
>>> framework *is* the native use case for this data structure.
>> We have at least:
>> linux/fb.h:
>> union {
>> char __iomem *screen_base; /* Virtual address */
>> char *screen_buffer;
>> };
>>
>> Which solve more or less the same problem.
I thought this was for convenience. The important is_iomem bit is missing.
>
> I also already noted that in TTM we have exactly the same problem and a
> whole bunch of helpers to allow operations on those pointers.
How do you call this within TTM?
The data structure represents a pointer to either system or I/O memory,
but not necessatrily device memory. It contains raw data. That would
give something like
struct databuf_map
struct databuf_ptr
struct dbuf_map
struct dbuf_ptr
My favorite would be dbuf_ptr. It's short and the API names would make
sense: dbuf_ptr_clear() for clearing, dbuf_ptr_set_vaddr() to set an
address, dbuf_ptr_incr() to increment, etc. Also, the _ptr indicates
that it's a single address; not an offset with length.
Best regards
Thomas
>
> Christian.
>
>>
>>
>>> Anyway, if a better name than dma-buf-map comes in, I'm willing to
>>> rename the thing. Otherwise I intend to merge the patchset by the end of
>>> the week.
>> Well, the main thing is that I think this shoud be moved away from
>> dma-buf. But if indeed dma-buf is the only relevant user in drm then
>> I am totally fine with the current naming.
>>
>> One alternative named that popped up in my head: struct sys_io_map {}
>> But again, if this is kept in dma-buf then I am fine with the current
>> naming.
>>
>> In other words, if you continue to think this is mostly a dma-buf
>> thing all three patches are:
>> Acked-by: Sam Ravnborg <sam@xxxxxxxxxxxx>
>>
>> Sam
>
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--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer
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