Re: [PATCH v3] crypto/caam: add backlogging support

["Horia Geantă" <horia.geanta@freescale.com>]

On 9/19/2015 12:02 PM, Alex Porosanu wrote:
> caam_jr_enqueue() function returns -EBUSY once there are no
> more slots available in the JR, but it doesn't actually save
> the current request. This breaks the functionality of users
> that expect that even if there is no more space for the request,
> it is at least queued for later execution. In other words, all
> crypto transformations that request backlogging
> (i.e. have CRYPTO_TFM_REQ_MAY_BACKLOG set), will hang. Such an
> example is dm-crypt.
> The current patch solves this issue by setting a threshold after
> which caam_jr_enqueue() returns -EBUSY, but since the HW job ring
> isn't actually full, the job is enqueued.
> Caveat: if the users of the driver don't obey the API contract which
> states that once -EBUSY is received, no more requests are to be
> sent, eventually the driver will reject the enqueues.
> For well-behaved CryptoAPI users, like dm-crypt, this is not the
> case, since the processing thread will sleep once -EBUSY is
> received.
> 
> Signed-off-by: Alex Porosanu <alexandru.porosanu@freescale.com>
> 
> ---
> v3:
> - as per Herbert's observation, allow only # of backlogging slots
>   transformations w/MAY_BACKLOG flag set to be affined to a JR;
>   the total # of transformations that can be thus allocated is equal
>   to the # of JRs times the # of "backlogging slots". In the standard
>   configuration, this means 16 x 4 = 64 transformations.

This won't work, since CRYPTO_TFM_REQ_MAY_BACKLOG is set per request (at
request setup time), not per tfm.

Horia