Re: [PATCH v2 01/12] mmc: add none blocking mmc request function

[David Vrabel <david.vrabel@csr.com>]

On 20/04/11 08:17, Per Forlin wrote:
> 
>> Using a MMC request queue has other benefits -- it allows multiple users
>> without having to claim/release the host.  This would be useful for
>> (especially multi-function) SDIO.
>
> You mean claim and release would be done only within the mmc core. The
> timed saved here would equal the time it takes to release and claim
> the host.
> Claim and release can also be used for power management to indicate if
> any client is using the host, if not the power can be switched off.

Isn't there a separate runtime power management API that different from
claim/release?

> I just want to make sure I understand the multi-function SDIO case, I
> haven't done any work with SDIO.
> Can the SDIO functions compete over the same claim_host at the same time?
> Example: if function 1 claims the host, function 2 and function 3 also
> want to claim the host but have to wait for function 1 to release the
> host.

This is the case.   Each function driver has to claim exclusive access
to the host.

> What is the extra benefit of having the internal request queue for
> multi function SDIO?

It reduces the delays between commands if multiple drivers are sending
commands.  I estimated performance improvements with 2-3% from just
removing the need to claim/release in one particular SDIO function
driver.  Performance improvements for multi-function cards would be a
bit more (5% perhaps?).

The more important benefit is the simplification of the API.

David
-- 
David Vrabel, Senior Software Engineer, Drivers
CSR, Churchill House, Cambridge Business Park,  Tel: +44 (0)1223 692562
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