Hi Marc & Raymond, Marc Zyngier <marc.zyngier@xxxxxxx> wrote on Thu, 23 May 2019 10:26:01 +0100: > On 23/05/2019 04:11, raymond pang wrote: > > Hi Miquel, > > > > This patch adds clearing GHC.IS into hot path, could you explain how > > irq storm is generated? thanks > > According to AHCI Spec, HBA should not refer to GHC.IS to generate > > MSI when applying multiple MSIs. > > Well spotted. > > I have the ugly feeling that this is because the Marvell AHCI > implementation is not using MSIs at all, but instead a pair of wired > interrupts (which are level triggered instead of edge, hence the > screaming interrupts). > > The changes in the following patches abuse the rest of the driver by > pretending this is a a multi-MSI setup, while it clearly doesn't match > the expectation of the AHCI spec for MSIs. > > It looks like this shouldn't be imposed on other unsuspecting > implementations which correctly use edge-triggered MSIs and do not > require such an MMIO access. I understand your concern, let me add a AHCI_HFLAG_LEVEL_MSI in hpriv->flags which will be used by the mvebu_ahci.c driver to request for this MMIO access. This way, the hot path remains the same. Thanks, Miquèl
