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SubjectRe: [PATCH] dmaengine: qcom: bam_dma: Add LOCK and UNLOCK flag bit support
On 2021-02-01 12:13, Vinod Koul wrote:
> On 01-02-21, 11:52, mdalam@codeaurora.org wrote:
>> On 2021-02-01 11:35, Vinod Koul wrote:
>> > On 27-01-21, 23:56, mdalam@codeaurora.org wrote:
>
>> > > 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.
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.

>
> 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.

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







> Thanks

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