linux-kernel - RE: [PATCH V3 02/12] misc: xilinx-sdfec: add core driver

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Date:   Fri, 3 May 2019 16:41:21 +0000
From:   Dragan Cvetic <draganc@...inx.com>
To:     Greg KH <gregkh@...uxfoundation.org>
CC:     "arnd@...db.de" <arnd@...db.de>, Michal Simek <michals@...inx.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Derek Kiernan <dkiernan@...inx.com>
Subject: RE: [PATCH V3 02/12] misc: xilinx-sdfec: add core driver

Hi Greg,

Please find my inline comments below,

Regards
Dragan

> -----Original Message-----
> From: Greg KH [mailto:gregkh@...uxfoundation.org]
> Sent: Thursday 2 May 2019 18:20
> To: Dragan Cvetic <draganc@...inx.com>
> Cc: arnd@...db.de; Michal Simek <michals@...inx.com>; linux-arm-kernel@...ts.infradead.org; robh+dt@...nel.org;
> mark.rutland@....com; devicetree@...r.kernel.org; linux-kernel@...r.kernel.org; Derek Kiernan <dkiernan@...inx.com>
> Subject: Re: [PATCH V3 02/12] misc: xilinx-sdfec: add core driver
> 
> On Sat, Apr 27, 2019 at 11:04:56PM +0100, Dragan Cvetic wrote:
> > +#define DRIVER_NAME "xilinx_sdfec"
> > +#define DRIVER_VERSION "0.3"
> 
> Version means nothing with the driver in the kernel tree, please remove
> it.

Will be removed. Thank you.

> 
> > +#define DRIVER_MAX_DEV BIT(MINORBITS)
> 
> Why this number?  Why limit yourself to any number?
> 

There can be max 8 devices for this driver. I'll change to 8.

> > +
> > +static struct class *xsdfec_class;
> 
> Do you really need your own class?

When writing a character device driver, my goal is to create and register an instance
of that structure associated with a struct file_operations, exposing a set of operations
to the user-space. One of the steps to make this goal is Create a class for a devices,
visible in /sys/class/.

> 
> > +static atomic_t xsdfec_ndevs = ATOMIC_INIT(0);
> 
> Why?

At the end this become a minor number. 
It is not needed, will be removed. Thanks.

> 
> > +static dev_t xsdfec_devt;
> 
> Why?
> 
> Why not use misc_device for this?  Why do you need your own major with a
> bunch of minor devices reserved ahead of time?  Why not just create a
> new misc device for every individual device that happens to be found in
> the system?  That will make the code a lot simpler and smaller and
> easier.
>
> 
> 
> > +
> > +/**
> > + * struct xsdfec_dev - Driver data for SDFEC
> > + * @regs: device physical base address
> > + * @dev: pointer to device struct
> > + * @config: Configuration of the SDFEC device
> > + * @open_count: Count of char device being opened
> > + * @xsdfec_cdev: Character device handle
> > + * @irq_lock: Driver spinlock
> > + *
> > + * This structure contains necessary state for SDFEC driver to operate
> > + */
> > +struct xsdfec_dev {
> > +	void __iomem *regs;
> > +	struct device *dev;
> > +	struct xsdfec_config config;
> > +	atomic_t open_count;
> > +	struct cdev xsdfec_cdev;
> > +	/* Spinlock to protect state_updated and stats_updated */
> > +	spinlock_t irq_lock;
> > +};
> > +
> > +static const struct file_operations xsdfec_fops = {
> > +	.owner = THIS_MODULE,
> > +};
> 
> No operations at all?  That's an easy driver :)


The operations are implemented in the later patches.


> 
> thanks,
> 
> greg k-h