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

[Oleksandr Shamray]

> -----Original Message-----
> From: Chip Bilbrey [mailto:chip@xxxxxxxxxxx]
> Sent: Monday, November 6, 2017 12:33 AM
> To: Oleksandr Shamray <oleksandrs@xxxxxxxxxxxx>
> Cc: gregkh@xxxxxxxxxxxxxxxxxxx; arnd@xxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> devicetree@xxxxxxxxxxxxxxx; openbmc@xxxxxxxxxxxxxxxx; joel@xxxxxxxxx;
> jiri@xxxxxxxxxxx; tklauser@xxxxxxxxxx; linux-serial@xxxxxxxxxxxxxxx;
> mec@xxxxxxxxx; Vadim Pasternak <vadimp@xxxxxxxxxxxx>; system-sw-low-
> level <system-sw-low-level@xxxxxxxxxxxx>; robh+dt@xxxxxxxxxx; openocd-
> devel-owner@xxxxxxxxxxxxxxxxxxxxx; linux-api@xxxxxxxxxxxxxxx;
> davem@xxxxxxxxxxxxx; mchehab@xxxxxxxxxx; Jiri Pirko <jiri@xxxxxxxxxxxx>
> 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@xxxxxxxxxxxxxxxxxxx>. 

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