linux-kernel - Re: [PATCH V9 XDMA 1/2] dmaengine: xilinx: xdma: Add xilinx xdma driver

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Message-ID: <4d4acb1f-f53a-2a1c-8172-3ea6edbd352f@amd.com>
Date:   Mon, 14 Nov 2022 08:55:36 -0800
From:   Lizhi Hou <lizhi.hou@....com>
To:     Vinod Koul <vkoul@...nel.org>
CC:     <dmaengine@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <trix@...hat.com>, <tumic@...see.org>, <max.zhen@....com>,
        <sonal.santan@....com>, <larry.liu@....com>, <brian.xu@....com>
Subject: Re: [PATCH V9 XDMA 1/2] dmaengine: xilinx: xdma: Add xilinx xdma
 driver


On 11/8/22 09:55, Lizhi Hou wrote:
>
> On 11/5/22 00:17, Vinod Koul wrote:
>> On 04-11-22, 11:17, Lizhi Hou wrote:
>>> On 11/4/22 10:57, Vinod Koul wrote:
>>>> On 04-11-22, 09:57, Lizhi Hou wrote:
>>>>> On 11/4/22 07:32, Vinod Koul wrote:
>>>>>> On 25-10-22, 10:57, Lizhi Hou wrote:
>>>>>>> +static inline int xdma_write_reg(struct xdma_device *xdev, u32 
>>>>>>> base, u32 reg,
>>>>>>> +                 u32 val)
>>>>>>> +{
>>>>>>> +    return regmap_write(xdev->regmap, base + reg, val);
>>>>>>> +}
>>>>>> Do you really need one more level indirection?
>>>>> Do you mean using readl / writel instead of regmap_* here?
>>>> Nope, I refer to using regmap_write() intead of xdma_write_reg()
>>> Ok. As you mentioned below,
>>>
>>>     why not move err into xdma_write_reg(), rather than adding in each
>>>     helper!
>>>
>>> If I use regmap_write() directly, I will not be able to move err into
>>> xdma_write_reg(). Having a inline function might be useful to add debug
>>> code.  May I keep xdma_write_reg()?
>> Okay, either way if xdma_write_reg() is doing only regmap_write() then
>> no, if it has extra logic like logging on error etc then it makes sense
> Got it. Thanks. :)
>>
>>>>>>> +failed:
>>>>>>> +    xdma_free_desc(&sw_desc->vdesc);
>>>>>> who will free sw_desc here?
>>>>> sw_desc is freed by xdma_free_desc(). xdma_free_desc() is virt-dma 
>>>>> callback
>>>>> it converts struct virt_dma_desc pointer to driver sw_desc pointer 
>>>>> and free
>>>>> the whole thing.
>>>> IN case of error, you are returning NULL, so allocated descriptor 
>>>> leaks
>>> I meant the descriptor is freed inside xdma_free_desc() which is called
>>> before 'return NULL'.
>>>
>>> xdma_free_desc(struct virt_dma_desc *vdesc)
>>>
>>> {
>>>
>>>          sw_desc = to_xdma_desc(vdesc);
>>>
>>>          .....
>>>
>>>          kfree(sw_desc);
>>>
>>> }
>> ok
>>
>>>>>>> +#ifndef _PLATDATA_AMD_XDMA_H
>>>>>>> +#define _PLATDATA_AMD_XDMA_H
>>>>>>> +
>>>>>>> +#include <linux/dmaengine.h>
>>>>>>> +
>>>>>>> +/**
>>>>>>> + * struct xdma_chan_info - DMA channel information
>>>>>>> + *    This information is used to match channel when request 
>>>>>>> dma channel
>>>>>>> + * @dir: Channel transfer direction
>>>>>>> + */
>>>>>>> +struct xdma_chan_info {
>>>>>>> +    enum dma_transfer_direction dir;
>>>>>>> +};
>>>>>>> +
>>>>>>> +#define XDMA_FILTER_PARAM(chan_info)    ((void *)(chan_info))
>>>>>>> +
>>>>>>> +struct dma_slave_map;
>>>>>>> +
>>>>>>> +/**
>>>>>>> + * struct xdma_platdata - platform specific data for XDMA engine
>>>>>>> + * @max_dma_channels: Maximum dma channels in each direction
>>>>>>> + */
>>>>>>> +struct xdma_platdata {
>>>>>>> +    u32 max_dma_channels;
>>>>>>> +    u32 device_map_cnt;
>>>>>>> +    struct dma_slave_map *device_map;
>>>>>>> +};
>>>>>> why do you need this plat data
>>>>> max_dma_channels is used to specify the maximum dma channels will 
>>>>> be used.
>>>> What is the device mode, who creates this dma device, devicetree or
>>>> something else?
>>> This dma engine is on PCI device (exposed on PCI BAR). Thus, the pci 
>>> device
>>> driver creates this dma device.
>> So it is a platform_device type? Why not make it something like auxdev?
>
> With our FPGA device, the XDMA IP is populated by flattened device 
> tree. Using platform device will support both device tree and non-dt 
> case.

Hi Vinod,

I am going to send out V10 patches to address other comments. Please let 
me know if you have more comments on this.


Thanks,

Lizhi

>
>
> Thanks,
> Lizhi
>
>>