From mboxrd@z Thu Jan 1 00:00:00 1970 From: "gregkh@linuxfoundation.org" Subject: Re: [v11,1/4] drivers: jtag: Add JTAG core driver Date: Tue, 14 Nov 2017 12:10:46 +0100 Message-ID: <20171114111046.GA23820@kroah.com> References: <1509724449-26221-2-git-send-email-oleksandrs@mellanox.com> <8760aoz78q.fsf@bilbrey.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Oleksandr Shamray Cc: 'Chip Bilbrey' , "arnd@arndb.de" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "devicetree@vger.kernel.org" , "openbmc@lists.ozlabs.org" , "joel@jms.id.au" , "jiri@resnulli.us" , "tklauser@distanz.ch" , "linux-serial@vger.kernel.org" , "mec@shout.net" , "robh+dt@kernel.org" , "openocd-devel-owner@lists.sourceforge.net" , "linux-api@vger.kernel.org" , "davem@davemloft.net" List-Id: devicetree@vger.kernel.org On Tue, Nov 14, 2017 at 10:34:49AM +0000, Oleksandr Shamray wrote: > > -----Original Message----- > > From: Chip Bilbrey [mailto:chip@bilbrey.org] > > Sent: Monday, November 6, 2017 12:33 AM > > To: Oleksandr Shamray > > Cc: gregkh@linuxfoundation.org; arnd@arndb.de; linux- > > kernel@vger.kernel.org; linux-arm-kernel@lists.infradead.org; > > devicetree@vger.kernel.org; openbmc@lists.ozlabs.org; joel@jms.id.au; > > jiri@resnulli.us; tklauser@distanz.ch; linux-serial@vger.kernel.org; > > mec@shout.net; Vadim Pasternak ; system-sw-low- > > level ; robh+dt@kernel.org; openocd- > > devel-owner@lists.sourceforge.net; linux-api@vger.kernel.org; > > davem@davemloft.net; mchehab@kernel.org; Jiri Pirko > > 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 . I asked to drop it as you didn't even implement it to work correctly :) > 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)) { You would stall an open? Why not just return saying you can't do that? Anyway, if you want to only have one access to the device at a time, great, but do it in a way that works properly. thanks, greg k-h