Re: [Qemu-devel] [PATCH v1 1/1] spapr_pci: remove all child functions in function zero unplug

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Aug 22, 2019 at 04:59:18PM -0300, Daniel Henrique Barboza wrote:
> There is nothing wrong with how sPAPR handles multifunction PCI
> hot unplugs. The problem is that x86 does it simpler. Instead of
> removing each non-zero function and then removing function zero,
> x86 can remove any function of the slot to trigger the hot unplug.
> 
> Libvirt will be directly impacted by this difference, in the
> (hopefully soon) PCI Multifunction hot plug/unplug support. For
> hot plugs, both x86 and sPAPR will operate the same way: a XML
> with all desired functions to be added, then consecutive hotplugs
> of all non-zero functions first, zero last. For hot unplugs, at
> least in the current state, a XML with the devices to be removed
> must also be provided because of how sPAPR operates - x86 does
> not need it - since any function unplug will unplug the whole
> PCIe slot. This difference puts extra strain in the management
> layer, which needs to either handle both archs differently in
> the unplug scenario or choose treat x86 like sPAPR, forcing x86
> users to cope with sPAPR internals.
> 
> This patch changes spapr_pci_unplug_request to handle the
> unplug of function zero differently. When removing function zero,
> instead of error-ing out if there are any remaining function
> DRCs which needs detaching, detach those. This has no effect in
> any existing scripts that are detaching the non-zero functions
> before function zero, and can be used by management as a shortcut
> to remove the whole PCI multifunction device without specifying
> each child function.

Makes sense to me, applied to ppc-for-4.2.

> 
> Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
> ---
>  hw/ppc/spapr_pci.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
> index deb0b0c80c..9f176f463e 100644
> --- a/hw/ppc/spapr_pci.c
> +++ b/hw/ppc/spapr_pci.c
> @@ -1700,11 +1700,13 @@ static void spapr_pci_unplug_request(HotplugHandler *plug_handler,
>                  state = func_drck->dr_entity_sense(func_drc);
>                  if (state == SPAPR_DR_ENTITY_SENSE_PRESENT
>                      && !spapr_drc_unplug_requested(func_drc)) {
> -                    error_setg(errp,
> -                               "PCI: slot %d, function %d still present. "
> -                               "Must unplug all non-0 functions first.",
> -                               slotnr, i);
> -                    return;
> +                    /*
> +                     * Attempting to remove function 0 of a multifunction
> +                     * device will will cascade into removing all child
> +                     * functions, even if their unplug weren't requested
> +                     * beforehand.
> +                     */
> +                    spapr_drc_detach(func_drc);
>                  }
>              }
>          }

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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