[PATCH 0/3] firewire: assist unit driver to compute packet timestamp

[Takashi Sakamoto]

Hi Stefan,

I'm sorry to post messages several times for the patchset if you are
still busy. But I'm still waiting for any reaction.

I note that Linus have announced merge window for v5.17 kernel.
 * https://lore.kernel.org/lkml/CAHk-=wgUkBrUVhjixy4wvrUhPbW-DTgtQubJWVOoLW=O0wRKMA@mail.gmail.com/T/#u

I'm glad if seeing your action for pull request as a response to the
window.


Kind Regards

Takashi Sakamoto

On Fri, Jan 07, 2022 at 08:01:18PM +0900, Takashi Sakamoto wrote:
> Hi Stefan,
> 
> Wishing you a happy new year.
> 
> We are in the last week for release of v5.16 kernel, and soon merge
> window for v5.17 kernel will be opened if thing goes well. I wish any
> action for the review process to merge these patches into upstream.
> 
> 
> Thanks
> 
> Takashi Sakamoto
> 
> On Tue, Dec 21, 2021 at 07:54:42PM +0900, Takashi Sakamoto wrote:
> > Hi Stefan,
> > 
> > Thank you for your long effort to maintain Linux FireWire subsystem. I'd
> > like to use the timestamp function for my integration in ALSA firewire
> > stack planned at next version of Linux kernel. I'm glad if getting to
> > your help for upstreaming.
> > 
> > On Thu, Dec 02, 2021 at 08:34:54PM +0900, Takashi Sakamoto wrote:
> > > Hi,
> > > 
> > > In 1394 OHCI specification, each descriptor of IR/IT/AR/AT DMA context
> > > has timeStamp field. The value of timeStamp field express the time in
> > > which the controller accept packet. The resolution of value is isochronous
> > > cycle count (8,000 Hz) with second up to 7.
> > > 
> > > I have a plan to use the value of timeStamp field for ALSA firewire stack
> > > so that userspace ALSA PCM/Rawmidi applications can get converted timestamp
> > > (ktime) for PCM frame/MIDI message. The timestamp can ideally express
> > > finer granularity than the time to invoke IRQ handler (and co).
> > > 
> > > Current implementation of Linux FireWire subsystem delivers the value of
> > > timeStamp field to unit driver for IR/IT/AT DMA context, but not for AR
> > > DMA context. Additionally, the way to refer to Isochronous Cycle Timer
> > > Register in MMIO region of 1394 OHCI controller is transaction to local
> > > node. It includes overhead of transaction and it's preferable to add
> > > less-overhead way available in any type of IRQ context.
> > > 
> > > This patchset adds two functions exposed in kernel space:
> > > 
> > >  * fw_card_read_cycle_time()
> > >     * allow unit driver to access to CYCLE_TIME register in MMIO region
> > >       without initiate transaction
> > >  * fw_request_get_timestamp()
> > >     * allow unit driver to get timestamp of request packet inner request
> > >       handler
> > > 
> > > I note that Hector Martin found kernel null pointer dereference during
> > > process to remove PCI card and has posted a patch:
> > > 
> > >  * https://lore.kernel.org/lkml/20211027113130.8802-1-marcan@marcan.st/
> > > 
> > > His patch is included in the series with my comment for relevant commit
> > > 20802224298c ("firewire: core: add forgotten dummy driver methods, remove
> > > unused ones"). The patch is required since unit driver can refer to dummy
> > > driver between removal callback of PCI subsystem and removal callback of
> > > FireWire subsystem.
> > > 
> > > Hector Martin (1):
> > >   firewire: Add dummy read_csr/write_csr functions
> > > 
> > > Takashi Sakamoto (2):
> > >   firewire: add kernel API to access CYCLE_TIME register
> > >   firewire: add kernel API to access packet structure in request
> > >     structure for AR context
> > > 
> > >  drivers/firewire/core-card.c        | 39 +++++++++++++++++++++++++++++
> > >  drivers/firewire/core-cdev.c        |  6 +++--
> > >  drivers/firewire/core-transaction.c | 18 +++++++++++++
> > >  include/linux/firewire.h            |  3 +++
> > >  4 files changed, 64 insertions(+), 2 deletions(-)
> > > 
> > > -- 
> > > 2.32.0
> > 
> > 
> > Sincerely yours
> > 
> > Takashi Sakamoto