On Mon 01 Feb 09:50 CST 2021, mdalam@codeaurora.org wrote:

On 2021-02-01 12:13, Vinod Koul wrote:

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On 01-02-21, 11:52, mdalam@codeaurora.org wrote:

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On 2021-02-01 11:35, Vinod Koul wrote:

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On 27-01-21, 23:56, mdalam@codeaurora.org wrote:

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  The actual LOCK/UNLOCK flag should be set on hardware command
descriptor.
  so this flag setting should be done in DMA engine driver. The user
of the
DMA
  driver like (in case of IPQ5018) Crypto can use flag
"DMA_PREP_LOCK" &
"DMA_PREP_UNLOCK"
  while preparing CMD descriptor before submitting to the DMA
engine. In DMA
engine driver
  we are checking these flasgs on CMD descriptor and setting actual
LOCK/UNLOCK flag on hardware
  descriptor.

I am not sure I comprehend this yet.. when is that we would need to do
this... is this for each txn submitted to dmaengine.. or something
else..

 Its not for each transaction submitted to dmaengine. We have to set
this
only
 once on CMD descriptor. So when A53 crypto driver need to change
the crypto
configuration
 then first it will lock the all other pipes using setting the LOCK
flag bit
on CMD
 descriptor and then it can start the transaction , on data
descriptor this
flag will
 not get set once all transaction will be completed the A53 crypto
driver
release the lock on
 all other pipes using UNLOCK flag on CMD descriptor. So LOCK/UNLOCK
will be
only once and not for
 the each transaction.

Okay so why cant the bam driver check cmd descriptor and do lock/unlock
as below, why do we need users to do this.

        if (flags & DMA_PREP_CMD) {
                do_lock_bam();

 User will not decide to do this LOCK/UNLOCK mechanism. It depends on
 use case.  This LOCK/UNLOCK mechanism not required always. It needs
 only when hardware will be shared between different core with
 different driver.

So you have a single piece of crypto hardware and you're using the BAM's
LOCK/UNLOCK feature to implement a "mutex" on a particular BAM channel?

 The LOCK/UNLOCK flags provides SW to enter ordering between pipes
execution.
 (Generally, the BAM pipes are total independent from each other and work in
parallel manner).
 This LOCK/UNLOCK flags are part of actual pipe hardware descriptor.

 Pipe descriptor having the following flags:
 INT : Interrupt
 EOT: End of transfer
 EOB: End of block
 NWD: Notify when done
 CMD: Command
 LOCK: Lock
 UNLOCK: Unlock
 etc.

 Here the BAM driver is common driver for (QPIC, Crypto, QUP etc. in
IPQ5018)
 So here only Crypto will be shared b/w multiple cores so For crypto request
only the LOCK/UNLOCK
 mechanism required.
 For other request like for QPIC driver, QUPT driver etc. its not required.
So Crypto driver has to raise the flag for
 LOCK/UNLOCK while preparing CMD descriptor. The actual locking will happen
in BAM driver only using condition
 if (flags & DMA_PREP_CMD) {
     if (flags & DMA_PREP_LOCK)
        desc->flags |= cpu_to_le16(DESC_FLAG_LOCK);
 }

 So Crypto driver should set this flag DMA_PREP_LOCK while preparing CMD
descriptor.
 So LOCK should be set on actual hardware pipe descriptor with descriptor
type CMD.

It sounds fairly clear that the actual descriptor modification must
happen in the BAM driver, but the question in my mind is how this is
exposed to the DMAengine clients (e.g. crypto, QPIC etc).

What is the life span of the locked state? Do you always provide a
series of descriptors that starts with a LOCK and ends with an UNLOCK?
Or do you envision that the crypto driver provides a LOCK descriptor and
at some later point provides a UNLOCK descriptor?


Finally, this patch just adds the BAM part of things, where is the patch
that actually makes use of this feature?

Regards,
Bjorn

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The point here is that this seems to be internal to dma and should be
handled by dma driver.

  This LOCK/UNLOK flags are part of actual hardware descriptor so this
should be handled by BAM driver only.
  If we set condition like this
  if (flags & DMA_PREP_CMD) {
                do_lock_bam();
  Then LOCK/UNLOCK will be applied for all the CMD descriptor including
(QPIC driver, QUP driver , Crypto driver etc.).
  So this is not our intension. So we need to set this LOCK/UNLOCK only for
the drivers it needs. So Crypto driver needs
  locking mechanism so we will set LOCK/UNLOCK flag on Crypto driver request
only for other driver request like QPIC driver,
  QUP driver will not set this.

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Also if we do this, it needs to be done for specific platforms..

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Thanks