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

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Message-ID: <Y2YOHx3RBJxdx9xz@matsya>
Date:   Sat, 5 Nov 2022 12:47:51 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Lizhi Hou <lizhi.hou@....com>
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 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

> > > > > +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?

-- 
~Vinod