linux-kernel - Re: [patch v23 4/4] Documentation: jtag: Add ABI documentation

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Date:   Tue, 29 May 2018 15:08:45 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Oleksandr Shamray <oleksandrs@...lanox.com>
Cc:     arnd@...db.de, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        openbmc@...ts.ozlabs.org, joel@....id.au, jiri@...nulli.us,
        tklauser@...tanz.ch, linux-serial@...r.kernel.org,
        vadimp@...lanox.com, system-sw-low-level@...lanox.com,
        robh+dt@...nel.org, openocd-devel-owner@...ts.sourceforge.net,
        linux-api@...r.kernel.org, davem@...emloft.net, mchehab@...nel.org
Subject: Re: [patch v23 4/4] Documentation: jtag: Add ABI documentation

On Tue, May 29, 2018 at 02:49:05PM +0300, Oleksandr Shamray wrote:
> +++ b/Documentation/ABI/testing/jtag-dev
> @@ -0,0 +1,27 @@
> +What:		/dev/jtag[0-9]+
> +Date:		May 2018
> +KernelVersion:	4.18
> +Contact:	oleksandrs@...lanox.com
> +Description:
> +		The misc device files /dev/jtag* are the interface
> +		between JTAG master interface and userspace.
> +
> +		The ioctl(2)-based ABI is defined and documented in
> +		[include/uapi]<linux/jtag.h>.
> +
> +		The following file operations are supported:
> +
> +		open(2)
> +		The argument flag currently support only one access
> +		mode O_RDWR.

Your open call tests for nothing, don't worry about it here at all :)

> +
> +		ioctl(2)
> +		Initiate various actions.
> +		See the inline documentation in [include/uapi]<linux/jtag.h>
> +		for descriptions of all ioctls.
> +
> +		close(2)
> +		Stops and free up the I/O contexts that was associated
> +		with the file descriptor.

No, your close() does not do any of that.

> +
> +Users:		TBD

No users?  They why do we have this api at all?

> +open(), close()
> +-------
> +open() opens JTAG device. Only one open operation per JTAG device
> +can be performed. Two or more open for one device will return error.

Not true :)

> +
> +Open/Close  device:
> +- jtag_fd = open("/dev/jtag0", O_RDWR);
> +- close(jtag_fd);
> +
> +ioctl()
> +-------
> +All access operations to JTAG devices are erformed through ioctl interface.
> +The IOCTL interface supports these requests:
> +	JTAG_IOCRUNTEST - Force JTAG state machine to RUN_TEST/IDLE state
> +	JTAG_SIOCFREQ - Set JTAG TCK frequency
> +	JTAG_GIOCFREQ - Get JTAG TCK frequency
> +	JTAG_IOCXFER - send JTAG data Xfer
> +	JTAG_GIOCSTATUS - get current JTAG TAP status
> +	JTAG_SIOCMODE - set JTAG mode flags.
> +
> +JTAG_SIOCFREQ, JTAG_GIOCFREQ
> +------
> +Set/Get JTAG clock speed:
> +
> +	unsigned int jtag_fd;
> +	ioctl(jtag_fd, JTAG_SIOCFREQ, &frq);
> +	ioctl(jtag_fd, JTAG_GIOCFREQ, &frq);
> +
> +JTAG_IOCRUNTEST
> +------
> +Force JTAG state machine to RUN_TEST/IDLE state
> +
> +struct jtag_run_test_idle {
> +	__u8	reset;
> +	__u8	endstate;
> +	__u8	tck;
> +};
> +
> +reset: 0 - run IDLE/PAUSE from current state
> +	   1 - go through TEST_LOGIC/RESET state before IDLE/PAUSE

Are you sure your enums are these values?  You should explicitly set
them in your .h file to be positive.

thanks,

greg k-h