Message-ID: <ee275d37-5dda-205a-a897-7a61ad13b536@linux.intel.com>
Date:   Wed, 25 Nov 2020 18:39:24 +0800
From:   "Reddy, MallikarjunaX" <mallikarjunax.reddy@...ux.intel.com>
To:     Vinod Koul <vkoul@...nel.org>
Cc:     dmaengine@...r.kernel.org, devicetree@...r.kernel.org,
        robh+dt@...nel.org, linux-kernel@...r.kernel.org,
        andriy.shevchenko@...el.com, chuanhua.lei@...ux.intel.com,
        cheol.yong.kim@...el.com, qi-ming.wu@...el.com,
        malliamireddy009@...il.com, peter.ujfalusi@...com
Subject: Re: [PATCH v9 2/2] Add Intel LGM SoC DMA support.

Hi Vinod,

Thanks for the review comments, my comments inline.

On 11/25/2020 1:21 AM, Vinod Koul wrote:
> On 24-11-20, 00:29, Reddy, MallikarjunaX wrote:
>> Hi Vinod,
>>
>> Thanks for your valuable review comments. Please see my comments inline.
>>
>> On 11/21/2020 8:17 PM, Vinod Koul wrote:
>>> On 20-11-20, 19:30, Reddy, MallikarjunaX wrote:
>>>> Hi Vinod,
>>>>
>>>> Thanks for the review. My comments inline.
>>>>
>>>> On 11/19/2020 1:38 AM, Vinod Koul wrote:
>>>>> On 12-11-20, 13:38, Amireddy Mallikarjuna reddy wrote:
>>>>>> Add DMA controller driver for Lightning Mountain (LGM) family of SoCs.
>>>>>>
>>>>>> The main function of the DMA controller is the transfer of data from/to any
>>>>>> peripheral to/from the memory. A memory to memory copy capability can also
>>>>>> be configured.
>>>>>>
>>>>>> This ldma driver is used for configure the device and channnels for data
>>>>>> and control paths.
>>>>>>
>>>>>> Signed-off-by: Amireddy Mallikarjuna reddy <mallikarjunax.reddy@...ux.intel.com>
>>>>>> ---
>>>>>> v1:
>>>>>> - Initial version.
>>>>> You have a cover letter, use that to keep track of these changes
>>>> ok.
>>>>>> +++ b/drivers/dma/lgm/Kconfig
>>>>>> @@ -0,0 +1,9 @@
>>>>>> +# SPDX-License-Identifier: GPL-2.0-only
>>>>>> +config INTEL_LDMA
>>>>>> +	bool "Lightning Mountain centralized low speed DMA and high speed DMA controllers"
>>>>> Do we have any other speeds :D
>>>> No other speeds :-)
>>> Right, so possibly drop the speed characterization here!
>> "Lightning Mountain centralized DMA controller"
>>>>>> +++ b/drivers/dma/lgm/lgm-dma.c
>>>>>> @@ -0,0 +1,1742 @@
>>>>>> +// SPDX-License-Identifier: GPL-2.0
>>>>>> +/*
>>>>>> + * Lightning Mountain centralized low speed and high speed DMA controller driver
>>>>>> + *
>>>>>> + * Copyright (c) 2016 ~ 2020 Intel Corporation.
>>>>> I think you mean 2016 - 2020, a dash which refers to duration
>>>> ok.
>>>>>> +struct dw2_desc {
>>>>>> +	struct {
>>>>>> +		u32 len		:16;
>>>>>> +		u32 res0	:7;
>>>>>> +		u32 bofs	:2;
>>>>>> +		u32 res1	:3;
>>>>>> +		u32 eop		:1;
>>>>>> +		u32 sop		:1;
>>>>>> +		u32 c		:1;
>>>>>> +		u32 own		:1;
>>>>>> +	} __packed field;
>>>>> Another one, looks like folks adding dmaengine patches love this
>>>>> approach, second one for the day..
>>>>>
>>>>> Now why do you need the bit fields, why not use register defines and
>>>>> helpers in bitfield.h to help configure the fields See FIELD_GET,
>>>>> FIELD_PREP etc
>>>> Let me check on this...
>>>>>> +struct dma_dev_ops {
>>>>>> +	int (*device_alloc_chan_resources)(struct dma_chan *chan);
>>>>>> +	void (*device_free_chan_resources)(struct dma_chan *chan);
>>>>>> +	int (*device_config)(struct dma_chan *chan,
>>>>>> +			     struct dma_slave_config *config);
>>>>>> +	int (*device_pause)(struct dma_chan *chan);
>>>>>> +	int (*device_resume)(struct dma_chan *chan);
>>>>>> +	int (*device_terminate_all)(struct dma_chan *chan);
>>>>>> +	void (*device_synchronize)(struct dma_chan *chan);
>>>>>> +	enum dma_status (*device_tx_status)(struct dma_chan *chan,
>>>>>> +					    dma_cookie_t cookie,
>>>>>> +					    struct dma_tx_state *txstate);
>>>>>> +	struct dma_async_tx_descriptor *(*device_prep_slave_sg)
>>>>>> +		(struct dma_chan *chan, struct scatterlist *sgl,
>>>>>> +		unsigned int sg_len, enum dma_transfer_direction direction,
>>>>>> +		unsigned long flags, void *context);
>>>>>> +	void (*device_issue_pending)(struct dma_chan *chan);
>>>>>> +};
>>>>> Heh! why do you have a copy of dmaengine ops here?
>>>> Ok, i will remove the ops and update the code accordingly.
>>>>>> +static int ldma_chan_desc_cfg(struct ldma_chan *c, dma_addr_t desc_base,
>>>>>> +			      int desc_num)
>>>>>> +{
>>>>>> +	struct ldma_dev *d = to_ldma_dev(c->vchan.chan.device);
>>>>>> +
>>>>>> +	if (!desc_num) {
>>>>>> +		dev_err(d->dev, "Channel %d must allocate descriptor first\n",
>>>>>> +			c->nr);
>>>>>> +		return -EINVAL;
>>>>>> +	}
>>>>>> +
>>>>>> +	if (desc_num > DMA_MAX_DESC_NUM) {
>>>>>> +		dev_err(d->dev, "Channel %d descriptor number out of range %d\n",
>>>>>> +			c->nr, desc_num);
>>>>>> +		return -EINVAL;
>>>>>> +	}
>>>>>> +
>>>>>> +	ldma_chan_desc_hw_cfg(c, desc_base, desc_num);
>>>>>> +
>>>>>> +	c->flags |= DMA_HW_DESC;
>>>>>> +	c->desc_cnt = desc_num;
>>>>>> +	c->desc_phys = desc_base;
>>>>> So you have a custom API which is used to configure this flag, a number
>>>>> and an address. The question is why, can you please help explain this?
>>>> LDMA used as general purpose dma(ver == DMA_VER22) and also supports DMA
>>>> capability for GSWIP in their network packet processing.( ver > DMA_VER22)
>>> Whats GSWIP?
>>>
>>>> Each Ingress(IGP) & Egress(EGP) ports of CQM use a dma channel.
>>> CQM?
>> GSWIP stands for  Gigabit Switch IP, and CQM is Central Queue Manager.
>>
>> GSWIP & CQM are the clients for the DMA. These are used in networking
>> purpose to increase transfer rates for peripheral like the GSWIP LAN switch.
> Please do add that when using these terms, folks outside Intel may not
> be aware of these terms.
Ok
>
>>>> desc needs to be configure for each dma channel and the remapped address of
>>>> the IGP & EGP is desc base adress.
>>> Why should this address not passed as src_addr/dst_addr?
>> src_addr/dst_addr is the data pointer. Data pointer indicates address
>> pointer of data buffer.
>>
>> ldma_chan_desc_cfg() carries the descriptor address.
>>
>> The descriptor list entry contains the data pointer, which points to the
>> data section in the memory.
>>
>> So we should not use src_addr/dst_addr as desc base address.
> Okay sounds reasonable. why is this using in API here?
descriptor base address needs to be write into the dma register (DMA_CDBA).
>
>>>> CQM client is using ldma_chan_desc_cfg() to configure the descriptior.
>>>>>> +static void dma_issue_pending(struct dma_chan *chan)
>>>>>> +{
>>>>>> +	struct ldma_chan *c = to_ldma_chan(chan);
>>>>>> +	struct ldma_dev *d = to_ldma_dev(c->vchan.chan.device);
>>>>>> +	unsigned long flags;
>>>>>> +
>>>>>> +	if (d->ver == DMA_VER22) {
>>>>> why is this specific to this version?
>>>> Only dma0 instance (ver == DMA_VER22) is used as a general purpose slave
>>>> DMA. we set both control and datapath here.
>>>> Other instances (ver > DMA_VER22) we set only control path. data path is
>>>> taken care by dma client(GSWIP).
>>>> Only thing needs to do is get the channel, set the descriptor and just 'ON'
>>>> the channel.
>>>>
>>>> CQM is highly low level register configurable/programmable take care about
>>>> the the packet processing through the register configurations.
>>> DMAengine fwk take care of channel management for clients and
>>> transaction management, if you not going to do transactions then why
>>> bother with dmaengine ?
>> dma0 instance (ver == DMA_VER22) uses DMAengine framework for both channel
>> management and transaction management.
>>
>> Other instances (ver > DMA_VER22) uses DMAengine mainly for channel
>> management.
>> To initiate the transaction client needs to ON the corresponding channel, So
>> dmaengine ops are using to 'ON'  and 'OFF' the channels.
> Is the addresses for transactions all hardcoded? WHo configures the
> transaction in (ver > DMA_VER22)
No, we are not using any hardcoded addresses.

client fills the the descriptor list entry and Once the descriptor base 
address write into register properly and ON the channel DMA transaction 
will be initiated.
>

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