On Thursday 10 November 2016 02:56 PM, Thomas Monjalon wrote: > 2016-11-10 14:40, Shreyansh Jain: >> On Thursday 10 November 2016 01:11 PM, Jianbo Liu wrote: >>> On 10 November 2016 at 14:10, Shreyansh Jain <shreyansh.jain at nxp.com> >>> wrote: >>>> On Thursday 10 November 2016 09:00 AM, Jianbo Liu wrote: >>>>> I'm still not sure about the purpose of soc_scan, and how to use it. >>>> >>>> >>>> For each device to be used by DPDK, which cannot be scanned/identified >>>> using >>>> the existing PCI/VDEV methods (sysfs/bus/pci), 'soc_scan_t' provides a way >>>> for driver to make those devices part of device lists. >>>> >>>> Ideally, 'scan' is not a function of a driver. It is a bus function - which >>>> is missing in this case. >>>> >>>>> If it's for each driver, it should at least struct rte_soc_driver * as >>>>> its parameter. >>>> >>>> >>>> Its for each driver - assuming that each non-PCI driver which implements it >>>> knows how to find devices which it can control (for example, special area >>>> in >>>> sysfs, or even platform bus). >>>> >>> >>> Considering there are several drivers in a platform bus, each driver >>> call the scan function, like the rte_eal_soc_scan_platform_bus() you >>> implemented. >>> The first will add soc devices to the list, but the remaining calls >>> are redundant. >> >> Indeed. This is exactly the issue we will face if we try and move this >> scan/match logic to PCI - all devices are identified in one step. >> >> There is a difference in principle here: >> A SoC device/driver combination is essentially focused towards a single >> type of bus<->devices. For example, a NXP PMD would implement a scan >> function which would scan for all devices on NXP's bus. This would not >> conflict with another XYZ SoC PMD which scans its specific bus. >> >> There is caveat to this - the platform bus. There can be multiple >> drivers which can serve platform bus compliant devices. First >> PMD->scan() initiated for such a bus/device would leave all other scans >> redundant. >> >> More similar caveats will come if we consider somewhat generic buses. At >> least I couldn't find any interest for such devices in the ML when I >> picked this series (from where Jan left it). >> >> Probably when more common type of PMDs come in, some default scan >> implementation can check for skipping those devices which are already >> added. It would be redundant but harmless. > > If several drivers use the same bus, it means the bus is standard enough > to be implemented in EAL. So the scan function of this bus should be > called only once when calling the generic EAL scan function. >
In the current model, without a bus like object, this can only be implemented as a hack. This is because: - If each driver has its scan, some of them (those on a common bus) would have their scan nullified - Then, EAL would initiate the scan on their behalf. (rte_eal_init) - Whereas, for those drivers which are 'special' scan, EAL would have to call each driver's scan. - This selection is manual code change (nullifying the scan function). - And then, EAL would have various 'generic' scan's chained together other than driver->scan(). A cleaner model would have been that EAL always calls the drivers->scan(). Obviously, this issue vanishes as soon as we have the bus->scan() like implementation where a bus would represent multiple devices/drivers. _________ Shreyansh
