Re: [PATCH v2 01/10] iommu/ipmmu-vmsa: Refactor micro-TLB lookup

Laurent Pinchart
2014-07-14T09:01:14Z

Hi Khiem,

On Monday 14 July 2014 09:19:23 Khiem Nguyen wrote:
> On 7/10/2014 7:37 PM, Laurent Pinchart wrote:
> > On Thursday 10 July 2014 09:03:26 Khiem Nguyen wrote:
> >> On 5/15/2014 7:40 PM, Laurent Pinchart wrote:
> >>> Cache the micro-TLB number in archdata allocated in the .add_device
> >>> handler instead of looking it up when the deviced is attached and
> >>> detached. This simplifies the .attach_dev and .detach_dev operations and
> >>> prepares for DT support.
> >>
> >> [snip]
> >>
> >>> Signed-off-by: Laurent Pinchart
> >>> <laurent.pinchart+renesas-ryLnwIuWjnjg/C1BVhZhaw@public.gmane.org>
> >>
> >> [snip]
> >>
> >>> +static int ipmmu_find_utlb(struct ipmmu_vmsa_device *mmu, struct device
> >>> *dev)
> >>> +{
> >>> + const struct ipmmu_vmsa_master *master = mmu->pdata->masters;
> >>> + const char *devname = dev_name(dev);
> >>> + unsigned int i;
> >>> +
> >>> + for (i = 0; i < mmu->pdata->num_masters; ++i, ++master) {
> >>> + if (strcmp(master->name, devname) == 0)
> >>> + return master->utlb;
> >>> + }
> >>> +
> >>> + return -1;
> >>> +}
> >>
> >> [snip]
> >>
> >>> static int ipmmu_add_device(struct device *dev)
> >>
> >> [snip]
> >>
> >>> list_for_each_entry(mmu, &ipmmu_devices, list) {
> >>> - master = ipmmu_find_master(mmu, dev);
> >>> - if (master) {
> >>> + utlb = ipmmu_find_utlb(mmu, dev);
> >>> + if (utlb >= 0) {
> >>> /*
> >>> - * TODO Take a reference to the master to protect
> >>> + * TODO Take a reference to the MMU to protect
> >>> * against device removal.
> >>> */
> >>> break;
> >>
> >> [snip]
> >>
> >>> + archdata->mmu = mmu;
> >>> + archdata->utlb = utlb;
> >>
> >> [snip]
> >>
> >> I have one question for ipmmu_add_device().
> >>
> >> In my understanding, your code will find utlb for device
> >> base on device name.
> >> For any device, it will /only/ return utlb number of first match.
> >>
> >> How about the case that a device name connected with more than 1 utlb ?
> >> e.g DU device (rcar-du-r8a7790) in Lager
> >>
> >> Was that case already covered in your code ?
> >
> > For the DU case, the R8A7790 contains /two DU devices/, each connected to
> > a single utlb. The IPMMU driver will thus work fine in that case.
>
> As my understanding, in board-lager-reference.c,
> DU devices are registered with 1 device name "rcar-du-r8a7790".
>
> I also added some logs in ipmmu_add_device() to observe
> the mapping between device name and utlb number.
> And I saw that only one utlb is mapped with DU.
>
> Do I miss anything here ?

No, you're right, my bad. This is definitely a limitation of the driver at the
moment.

> > I agree that this is a problem in general though, other devices (such as
> > the DMAC) are connected to more than one utlb. This is currently not
> > supported by the driver.
>
> Thanks for your confirmation.
> I guess the driver will be improved in near future.

Yes, it will.

--
Regards,

Laurent Pinchart