On Tuesday 09 September 2014 19:16:01 Lian Minghuan-B31939 wrote: > On 2014年09月09日 10:50, Arnd Bergmann wrote: > > On Tuesday 09 September 2014 18:46:59 Lian Minghuan-B31939 wrote: > >> On 2014年09月09日 09:56, Arnd Bergmann wrote: > >>> On Tuesday 09 September 2014 17:25:57 Lian Minghuan-B31939 wrote: > >>>> [Minghuan] I discussed with my colleague. They worry about performance > >>>> degradation if using regmap API, > >>>> because there are some fast device use scfg. We tend to use a simple way > >>>> to map andread/write scfg directly. > >>> I see. In this case, I would probably create a separate msi controller > >>> driver that owns the "fsl,ls1021a-scfg" device, and is referenced > >>> through the "msi-parent" property in the pcie controller. > >>> > >>> You can use of_pci_find_msi_chip_by_node() to get the msi_chip > >>> instance and then connect that to your pci host. This will also > >>> take care of the case where you may want to use the main GICv3 > >>> on a future SoC. > >> > >> [Minghuan] There is something wrong with LS1021A MSI hardware that it > >> only supports one interrupt not 32 interrupts. Now, I do not want to > >> create a separate msi controller driver just for incorrect hardware. > >> I may provide complete MSI driver for the new hardware when it is ready. > > > > Would you just leave out MSI support for the LS1021A PCIe variant? > > I guess that's fine because all device drivers should also support > > legacy interrupts and there is no performance gain in MSI in this > > case. > > [Minghuan] I have added MSI support for LS1021A PCIe just reserved 31 > interrupts as used. I don't understand your logic then. If LS1021A has an incorrect MSI implementation, and you may want to reuse the PCIe driver with a future chip that either includes a correct MSI implementation, or with one that uses the GICv3 instead, isn't that even more reason to split out the MSI support into a separate driver? That way you can at least separate the normal code path from the broken one and don't need any special run-time or compile-conditionals beyond calling of_pci_find_msi_chip_by_node(). Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
