linux-kernel - Re: [PATCH 1/2] dmaengine: ti: k3-udma: Respond TX done if DMA_PREP

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Date:   Sat, 10 Sep 2022 21:57:20 +0300
From:   Péter Ujfalusi <peter.ujfalusi@...il.com>
To:     Vaishnav Achath <vaishnav.a@...com>, vkoul@...nel.org,
        broonie@...nel.org, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org
Cc:     vigneshr@...com, kishon@...com
Subject: Re: [PATCH 1/2] dmaengine: ti: k3-udma: Respond TX done if
 DMA_PREP_INTERRUPT is not requested



On 05/09/2022 06:02, Vaishnav Achath wrote:
>> Let me think about over the weekend... Do you have performance numbers for this
>> change?
>>
> Thank you, yes we tested mainly for the SPI cases(Master and Slave mode), there
> we saw a peak delay of 400ms for transaction completion and this varied with CPU
> load, after adding the patch to not wait for DMA TX completion and use EOW
> interrupt the peak latency reduced to 2ms.

Thank you for the details.

>> If we make sure that this is only affecting non cyclic transfers with a in code
>> comment to explain the expectations from the user I think this can be safe.
>> \
> Sure I will add this in the next revision.

You can add my Acked-by when you send the next version:
Acked-by: Peter Ujfalusi <peter.ujfalusi@...il.com>

>>>
>>>>>
>>>>> Signed-off-by: Vaishnav Achath <vaishnav.a@...com>
>>>>> ---
>>>>>    drivers/dma/ti/k3-udma.c | 5 ++++-
>>>>>    1 file changed, 4 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/dma/ti/k3-udma.c b/drivers/dma/ti/k3-udma.c
>>>>> index 39b330ada200..03d579068453 100644
>>>>> --- a/drivers/dma/ti/k3-udma.c
>>>>> +++ b/drivers/dma/ti/k3-udma.c
>>>>> @@ -263,6 +263,7 @@ struct udma_chan_config {
>>>>>        enum udma_tp_level channel_tpl; /* Channel Throughput Level */
>>>>>          u32 tr_trigger_type;
>>>>> +    unsigned long tx_flags;
>>>>>          /* PKDMA mapped channel */
>>>>>        int mapped_channel_id;
>>>>> @@ -1057,7 +1058,7 @@ static bool udma_is_desc_really_done(struct udma_chan
>>>>> *uc, struct udma_desc *d)
>>>>>          /* Only TX towards PDMA is affected */
>>>>>        if (uc->config.ep_type == PSIL_EP_NATIVE ||
>>>>> -        uc->config.dir != DMA_MEM_TO_DEV)
>>>>> +        uc->config.dir != DMA_MEM_TO_DEV || !(uc->config.tx_flags &
>>>>> DMA_PREP_INTERRUPT))
>>>>>            return true;
>>>>>          peer_bcnt = udma_tchanrt_read(uc, UDMA_CHAN_RT_PEER_BCNT_REG);
>>>>> @@ -3418,6 +3419,8 @@ udma_prep_slave_sg(struct dma_chan *chan, struct
>>>>> scatterlist *sgl,
>>>>>        if (!burst)
>>>>>            burst = 1;
>>>>>    +    uc->config.tx_flags = tx_flags;
>>>>> +
>>>>>        if (uc->config.pkt_mode)
>>>>>            d = udma_prep_slave_sg_pkt(uc, sgl, sglen, dir, tx_flags,
>>>>>                           context);
>>>>
>>>
>>
> 

-- 
Péter