Re: [PATCH v5 09/17] dmaengine: sh: rz-dmac: Use virt-dma APIs for channel descriptor processing

[Claudiu Beznea <claudiu.beznea@kernel.org>]

Hi, Frank,

On 5/13/26 00:38, Frank Li wrote:
> On Tue, May 12, 2026 at 03:12:10PM +0300, Claudiu Beznea wrote:
>> The driver used a mix of virt-dma APIs and driver specific logic to
>> process descriptors. It maintained three internal queues: ld_free,
>> ld_queue, and ld_active as follows:
>> - ld_free: stores the descriptors pre-allocated at probe time
>> - ld_queue: stores descriptors after they are taken from ld_free and
>>    prepared. At the same time, vchan_tx_prep() queues them to
>>    vc->desc_allocated. The vc->desc_allocated list is then checked in
>>    rz_dmac_issue_pending() and rz_dmac_irq_handler_thread() before
>>    starting a new transfer via rz_dmac_xfer_desc(). In turn,
>>    rz_dmac_xfer_desc() grabs the next descriptor from vc->desc_issued and
>>    submits it for transfer
>> - ld_active: stores the descriptors currently being transferred
>>
>> The interrupt handler moved a completed descriptor to ld_free before
>> invoking its completion callback. Once returned to ld_free, the
>> descriptor can be reused to prepare a new transfer. In theory, this
>> means the descriptor could be re-prepared before its completion
>> callback is called.
>>
>> Commit fully back the driver by the virt-dma APIs. With this, only ld_free
>> need to be kept to track how many free descriptors are available. This
>> is now done as follows:
>> - the prepare stage removes the first descriptor from the ld_free and
>>    prepares it
>> - the completion calls for it vc->desc_free() (rz_dmac_virt_desc_free())
>>    which re-adds the descriptor at the end of ld_free
>>
>> With this, the critical areas in prepare callbacks were minimized to only
>> getting the descriptor from the ld_free list.
> 
> Do you plan remove ld_free also?

I thought about it. But I prefer to keep it aside from this set as it is already 
big enough and I haven't notice any possible issue with it.

> 
>>
>> This change introduces struct rz_dmac_chan::desc to keep track of the
> 
> Remove "this change", just Introduce ...

OK

-- 
Thank you,
Claudiu