From: Jonathan Matthew <jonathan@d14n.org>
Subject: Re: ahci(4): Disable PMP for AMD AHCI controler
To: Jan Klemkow <jan@openbsd.org>
Cc: tech@openbsd.org
Date: Tue, 21 Jul 2026 09:55:50 +1000

On Mon, Jul 20, 2026 at 08:17:33PM +0200, Jan Klemkow wrote:
> Hi,
> 
> The AMD AHCI controller advertises port multiplier support but probing
> for a PMP on each port costs 10 seconds of timeouts per disk at attach
> time.  We should disable it, like we do it for Intel.

What systems does this controller appear in?  Do you know if port
multipliers actually work with it? 

> 
> ok?
> 
> bye,
> jan
> 
> Index: dev/pci/ahci_pci.c
> ===================================================================
> RCS file: /cvs/src/sys/dev/pci/ahci_pci.c,v
> diff -u -p -r1.18 ahci_pci.c
> --- dev/pci/ahci_pci.c	16 Jun 2024 18:00:08 -0000	1.18
> +++ dev/pci/ahci_pci.c	20 Jul 2026 15:00:21 -0000
> @@ -67,6 +67,8 @@ int			ahci_ati_sb700_attach(struct ahci_
>  			    struct pci_attach_args *);
>  int			ahci_amd_hudson2_attach(struct ahci_softc *,
>  			    struct pci_attach_args *);
> +int			ahci_amd_kerncz_attach(struct ahci_softc *,
> +			    struct pci_attach_args *);
>  int			ahci_intel_attach(struct ahci_softc *,
>  			    struct pci_attach_args *);
>  int			ahci_samsung_attach(struct ahci_softc *,
> @@ -88,6 +90,11 @@ static const struct ahci_device ahci_dev
>  	{ PCI_VENDOR_AMD,	PCI_PRODUCT_AMD_HUDSON2_SATA_6,
>  	    NULL,		ahci_amd_hudson2_attach },
>  
> +	{ PCI_VENDOR_AMD,	PCI_PRODUCT_AMD_KERNCZ_AHCI_1,
> +	    NULL,		ahci_amd_kerncz_attach },
> +	{ PCI_VENDOR_AMD,	PCI_PRODUCT_AMD_KERNCZ_AHCI_2,
> +	    NULL,		ahci_amd_kerncz_attach },
> +
>  	{ PCI_VENDOR_ATI,	PCI_PRODUCT_ATI_SB600_SATA,
>  	    NULL,		ahci_ati_sb600_attach },
>  	{ PCI_VENDOR_ATI,	PCI_PRODUCT_ATI_SBX00_SATA_1,
> @@ -263,6 +270,14 @@ ahci_amd_hudson2_attach(struct ahci_soft
>  	ahci_ati_sb_idetoahci(sc, pa);
>  
>  	sc->sc_flags |= AHCI_F_IPMS_PROBE;
> +
> +	return (0);
> +}
> +
> +int
> +ahci_amd_kerncz_attach(struct ahci_softc *sc, struct pci_attach_args *pa)
> +{
> +	sc->sc_flags |= AHCI_F_NO_PMP;
>  
>  	return (0);
>  }
>