linux-kernel - Re: [patch v21 1/4] drivers: jtag: Add JTAG core driver

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Date:   Wed, 16 May 2018 00:21:35 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Oleksandr Shamray <oleksandrs@...lanox.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        devicetree <devicetree@...r.kernel.org>,
        openbmc@...ts.ozlabs.org, Joel Stanley <joel@....id.au>,
        Jiří Pírko <jiri@...nulli.us>,
        Tobias Klauser <tklauser@...tanz.ch>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Vadim Pasternak <vadimp@...lanox.com>,
        system-sw-low-level@...lanox.com, Rob Herring <robh+dt@...nel.org>,
        openocd-devel-owner@...ts.sourceforge.net,
        linux-api@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Jiri Pirko <jiri@...lanox.com>
Subject: Re: [patch v21 1/4] drivers: jtag: Add JTAG core driver

On Tue, May 15, 2018 at 5:21 PM, Oleksandr Shamray
<oleksandrs@...lanox.com> wrote:
> Initial patch for JTAG driver
> JTAG class driver provide infrastructure to support hardware/software
> JTAG platform drivers. It provide user layer API interface for flashing
> and debugging external devices which equipped with JTAG interface
> using standard transactions.
>
> Driver exposes set of IOCTL to user space for:
> - XFER:
> - SIR (Scan Instruction Register, IEEE 1149.1 Data Register scan);
> - SDR (Scan Data Register, IEEE 1149.1 Instruction Register scan);
> - RUNTEST (Forces the IEEE 1149.1 bus to a run state for a specified
>   number of clocks).
> - SIOCFREQ/GIOCFREQ for setting and reading JTAG frequency.
>
> Driver core provides set of internal APIs for allocation and
> registration:
> - jtag_register;
> - jtag_unregister;
> - jtag_alloc;
> - jtag_free;
>
> Platform driver on registration with jtag-core creates the next
> entry in dev folder:
> /dev/jtagX

>  0xB0   all     RATIO devices           in development:
>                                         <mailto:vgo@...io.de>
>  0xB1   00-1F   PPPoX                   <mailto:mostrows@...x.uwaterloo.ca>
> +0xB2   00-0f   linux/jtag.h            JTAG driver
> +                                       <mailto:oleksandrs@...lanox.com>

Consider to preserve style (upper vs. lower).

> +         This provides basic core functionality support for JTAG class devices.
> +         Hardware that is equipped with a JTAG microcontroller can be
> +         supported by using this driver's interfaces.
> +         This driver exposes a set of IOCTLs to the user space for
> +         the following commands:
> +         SDR: (Scan Data Register) Performs an IEEE 1149.1 Data Register scan
> +         SIR: (Scan Instruction Register) Performs an IEEE 1149.1 Instruction
> +         Register scan.
> +         RUNTEST: Forces the IEEE 1149.1 bus to a run state for a specified
> +         number of clocks or a specified time period.

Something feels wrong with formatting here.

> +#define MAX_JTAG_NAME_LEN (sizeof("jtag") + 5)

Interesting definition. Why not to set to 10 explicitly? And why 10?
(16 sounds better)

> +struct jtag {
> +       struct miscdevice miscdev;

> +       struct device *dev;

Doesn't miscdev parent contain exactly this one?

> +       const struct jtag_ops *ops;
> +       int id;
> +       bool opened;
> +       struct mutex open_lock;
> +       unsigned long priv[0];
> +};

> +               err = copy_to_user(u64_to_user_ptr(xfer.tdio),
> +                                  (void *)(xfer_data), data_size);

Redundant parens in one case. Check the rest similar places.

> +static int jtag_open(struct inode *inode, struct file *file)
> +{

> +       struct jtag *jtag = container_of(file->private_data, struct jtag,
> +                                        miscdev);

I would don't care about length and put it on one line.

> +       if (jtag->opened) {
> +       jtag->opened = true;
> +       jtag->opened = false;

Can it be opened non exclusively several times? If so, this needs to
be a ref counter instead.

> +       if (!ops->idle || !ops->mode_set || !ops->status_get || !ops->xfer)
> +               return NULL;

Are all of them mandatory?

> +int jtag_register(struct jtag *jtag)

Perhaps devm_ variant.

> +#define jtag_u64_to_ptr(arg) ((void *)(uintptr_t)arg)

Where is this used or supposed to be used?

> +#define JTAG_MAX_XFER_DATA_LEN 65535

Is this limitation from some spec?
Otherwise why not to allow 64K?

> +/**
> + * struct jtag_ops - callbacks for jtag control functions:
> + *
> + * @freq_get: get frequency function. Filled by device driver
> + * @freq_set: set frequency function. Filled by device driver
> + * @status_get: set status function. Filled by device driver
> + * @idle: set JTAG to idle state function. Filled by device driver
> + * @xfer: send JTAG xfer function. Filled by device driver
> + */

Perhaps you need to describe which of them are _really_ mandatory and
which are optional.

-- 
With Best Regards,
Andy Shevchenko