linux-kernel - Re: [PATCH v9 2/3] dmaengine: ptdma: register PTDMA controller as a DMA resource

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Date:   Wed, 16 Jun 2021 10:53:35 +0530
From:   Sanjay R Mehta <sanmehta@....com>
To:     Vinod Koul <vkoul@...nel.org>
Cc:     Sanjay R Mehta <Sanju.Mehta@....com>, gregkh@...uxfoundation.org,
        dan.j.williams@...el.com, Thomas.Lendacky@....com,
        Shyam-sundar.S-k@....com, Nehal-bakulchandra.Shah@....com,
        robh@...nel.org, mchehab+samsung@...nel.org, davem@...emloft.net,
        linux-kernel@...r.kernel.org, dmaengine@...r.kernel.org
Subject: Re: [PATCH v9 2/3] dmaengine: ptdma: register PTDMA controller as a
 DMA resource



On 6/16/2021 9:48 AM, Vinod Koul wrote:
> [CAUTION: External Email]
> 
> On 15-06-21, 17:04, Sanjay R Mehta wrote:
>>
>>
>> On 6/9/2021 12:26 AM, Vinod Koul wrote:
>>
>> [snipped]
>>
>>>> +static struct pt_dma_desc *pt_alloc_dma_desc(struct pt_dma_chan *chan,
>>>> +                                          unsigned long flags)
>>>> +{
>>>> +     struct pt_dma_desc *desc;
>>>> +
>>>> +     desc = kmem_cache_zalloc(chan->pt->dma_desc_cache, GFP_NOWAIT);
>>>> +     if (!desc)
>>>> +             return NULL;
>>>> +
>>>> +     vchan_tx_prep(&chan->vc, &desc->vd, flags);
>>>> +
>>>> +     desc->pt = chan->pt;
>>>> +     desc->issued_to_hw = 0;
>>>> +     INIT_LIST_HEAD(&desc->cmdlist);
>>>
>>> why do you need your own list, the lists in vc should suffice?
>>>
>>
>> Do you think this should be a major blocker for pulling this series in 5.14?
>> Would you be okay to accept this change in the subsequent driver updates?
> 
> Sorry that is not how upstream works, I would like things to be better
> before we merge this
> 

Sure Vinod, I will fix this and send the change in next version.

>>
>>>> +static int pt_resume(struct dma_chan *dma_chan)
>>>> +{
>>>> +     struct pt_dma_chan *chan = to_pt_chan(dma_chan);
>>>> +     struct pt_dma_desc *desc = NULL;
>>>> +     unsigned long flags;
>>>> +
>>>> +     spin_lock_irqsave(&chan->vc.lock, flags);
>>>> +     pt_start_queue(&chan->pt->cmd_q);
>>>> +     desc = __pt_next_dma_desc(chan);
>>>> +     spin_unlock_irqrestore(&chan->vc.lock, flags);
>>>> +
>>>> +     /* If there was something active, re-start */
>>>> +     if (desc)
>>>> +             pt_cmd_callback(desc, 0);
>>>
>>> this doesn't sound correct. In pause yoy stop the queue, so start of the
>>> queue should be done here... Why grab a descriptor?
>>>
>>>> +static int pt_terminate_all(struct dma_chan *dma_chan)
>>>> +{
>>>> +     struct pt_dma_chan *chan = to_pt_chan(dma_chan);
>>>> +
>>>> +     vchan_free_chan_resources(&chan->vc);
>>>
>>> what about the descriptors, are you not going to clear the lists and
>>> free them..
>>>
>>>> +int pt_dmaengine_register(struct pt_device *pt)
>>>> +{
>>>> +     struct pt_dma_chan *chan;
>>>> +     struct dma_device *dma_dev = &pt->dma_dev;
>>>> +     char *cmd_cache_name;
>>>> +     char *desc_cache_name;
>>>> +     int ret;
>>>> +
>>>> +     pt->pt_dma_chan = devm_kzalloc(pt->dev, sizeof(*pt->pt_dma_chan),
>>>> +                                    GFP_KERNEL);
>>>> +     if (!pt->pt_dma_chan)
>>>> +             return -ENOMEM;
>>>> +
>>>> +     cmd_cache_name = devm_kasprintf(pt->dev, GFP_KERNEL,
>>>> +                                     "%s-dmaengine-cmd-cache",
>>>> +                                     pt->name);
>>>> +     if (!cmd_cache_name)
>>>> +             return -ENOMEM;
>>>> +
>>>> +     pt->dma_cmd_cache = kmem_cache_create(cmd_cache_name,
>>>> +                                           sizeof(struct pt_dma_cmd),
>>>> +                                           sizeof(void *),
>>>> +                                           SLAB_HWCACHE_ALIGN, NULL);
>>>> +     if (!pt->dma_cmd_cache)
>>>> +             return -ENOMEM;
>>>> +
>>>> +     desc_cache_name = devm_kasprintf(pt->dev, GFP_KERNEL,
>>>> +                                      "%s-dmaengine-desc-cache",
>>>> +                                      pt->name);
>>>> +     if (!desc_cache_name) {
>>>> +             ret = -ENOMEM;
>>>> +             goto err_cache;
>>>> +     }
>>>> +
>>>> +     pt->dma_desc_cache = kmem_cache_create(desc_cache_name,
>>>> +                                            sizeof(struct pt_dma_desc),
>>>> +                                            sizeof(void *),
>>>
>>> sizeof void ptr?
> 
> This and many more comments are left not replied, do you agree to them,
> do you disagree, hard to tell from silence..
> 

Yes, I agree with all other comments and will send the changes in next
version of the patch series.

>>>
>>>> +                                            SLAB_HWCACHE_ALIGN, NULL);
>>>> +     if (!pt->dma_desc_cache) {
>>>> +             ret = -ENOMEM;
>>>> +             goto err_cache;
>>>> +     }
>>>> +
>>>> +     dma_dev->dev = pt->dev;
>>>> +     dma_dev->src_addr_widths = DMA_SLAVE_BUSWIDTH_64_BYTES;
>>>> +     dma_dev->dst_addr_widths = DMA_SLAVE_BUSWIDTH_64_BYTES;
>>>> +     dma_dev->directions = DMA_MEM_TO_MEM;
>>>> +     dma_dev->residue_granularity = DMA_RESIDUE_GRANULARITY_DESCRIPTOR;
>>>> +     dma_cap_set(DMA_MEMCPY, dma_dev->cap_mask);
>>>> +     dma_cap_set(DMA_INTERRUPT, dma_dev->cap_mask);
>>>> +     dma_cap_set(DMA_PRIVATE, dma_dev->cap_mask);
>>>
>>> Why DMA_PRIVATE ? this is a dma mempcy controller ...
>>
>> This DMA controller is intended to be used with AMD Non-Transparent
>> Bridge devices and not for general purpose peripheral DMA. Hence marking
>> it as DMA_PRIVATE.
> 
> Okay, maybe add a comment so that people would know
> 

Sure. I will add comment here.

> --
> ~Vinod
>