Re: [PATCH 1/5] spi: spi_lock_bus and spi_unlock_bus

[Grant Likely <grant.likely-s3s/WqlpOiPyB63q8FvJNQ@public.gmane.org>]

On Wed, Feb 17, 2010 at 6:30 AM, Grant Likely <grant.likely-s3s/WqlpOiPyB63q8FvJNQ@public.gmane.org> wrote:
> On Wed, Feb 17, 2010 at 12:35 AM, Ernst Schwab <mail-3FdAPXqljGQisWB6T/0fQA@public.gmane.org> wrote:
>> Grant Likely wrote:
>>
>>> It sounds like you're very worried about making changes to the core
>>> code,
>>
>> Maybe...
>>
>>> In fact, now that I've had an evening to think about it, the solution
>>> is even simpler than what I said earlier.  It requires 3 things to be
>>> added to struct spi_master.
>>> - 1 Mutex
>>> - 1 spin lock
>>> - 1 flag.
>>
>>> The mutex protects spi_async, and provides sleeping "for free"
>>> The spinlock protects the atomic spi_sync call.
>>
>> Sound viable and good, but, in Documentation/spi/spi-summary we have:
>>
>> "
>> The basic I/O primitive is spi_async().  Async requests may be
>> issued in any context (irq handler, task, etc) and completion
>> is reported using a callback provided with the message.
>> After any detected error, the chip is deselected and processing
>> of that spi_message is aborted.
>> "
>>
>> Is this compatible with a Mutex protecting spi_async?
>> It seems to me, that spi_async must queue the SPI message
>> immediately and return. The queue is implemented in the SPI master driver. I
>> suppose that's why the blackfin bus locking pioneers chose to make the
>> change in the SPI master driver.
>
> No, sorry, I made a mistake and got the functions backwards when I was
> writing up my description.  What I meant to say is:
>
> spi_sync() is protected by a mutex because it can sleep
> spi_async() needs to be protected with a flag and a spinlock because
> it can be called atomically and must not sleep

On that note, apparently I find sync/async easy to mix up.  I wonder
if other people find the same and if it would be a good idea to
migrate to clearer names.  Perhaps spi_submit() and
spi_submit_atomic().

g.

------------------------------------------------------------------------------
SOLARIS 10 is the OS for Data Centers - provides features such as DTrace,
Predictive Self Healing and Award Winning ZFS. Get Solaris 10 NOW
http://p.sf.net/sfu/solaris-dev2dev