[v11,1/4] drivers: jtag: Add JTAG core driver

[Oleksandr Shamray]

> -----Original Message-----
> From: Chip Bilbrey [mailto:chip at bilbrey.org]
> Sent: Monday, November 6, 2017 12:33 AM
> To: Oleksandr Shamray <oleksandrs at mellanox.com>
> Cc: gregkh at linuxfoundation.org; arnd at arndb.de; linux-
> kernel at vger.kernel.org; linux-arm-kernel at lists.infradead.org;
> devicetree at vger.kernel.org; openbmc at lists.ozlabs.org; joel at jms.id.au;
> jiri at resnulli.us; tklauser at distanz.ch; linux-serial at vger.kernel.org;
> mec at shout.net; Vadim Pasternak <vadimp at mellanox.com>; system-sw-low-
> level <system-sw-low-level at mellanox.com>; robh+dt at kernel.org; openocd-
> devel-owner at lists.sourceforge.net; linux-api at vger.kernel.org;
> davem at davemloft.net; mchehab at kernel.org; Jiri Pirko <jiri at mellanox.com>
> Subject: Re: [v11,1/4] drivers: jtag: Add JTAG core driver
> 
> 
> Oleksandr Shamray writes:

[..]

> I notice the single-open()-per-device lock was dropped by request in an earlier
> revision of your patches, but multiple processes trying to drive a single JTAG
> master could wreak serious havoc if transactions get interleaved. Would
> something like an added JTAG_LOCKCHAIN/UNLOCKCHAIN
> ioctl() for exclusive client access be reasonable to prevent this?
> 

Yes, it dropped by recommendation of Greg KH <gregkh at linuxfoundation.org>. 

Greg, what you can suggest about it. May be better to add again single-open()-per-device lock with right locking way like:

>if (mutex_lock_interruptible(&jtag->open_lock)) {
>	return -ERESTARTSYS;
>}
>
>if (jtag->opened) {
>	mutex_unlock(&jtag->open_lock);
>	return -EINVAL;
>}
>
>nonseekable_open(inode, file);
>file->private_data = jtag;
>jtag->opened++;
>mutex_unlock(&jtag->open_lock);
>

Thaks.

> -Chip