On 06/14/2016 06:42 PM, Vinod Koul wrote: > On Tue, Jun 14, 2016 at 11:02:29AM +0200, Lars-Peter Clausen wrote: >>> >>> ACPI has device tables which describe the devices which are not >>> discoverable. (not everything in x86 is discoverable) >>> >>> Yes these are hard coded in BIOS, but if you are connecting >>> FPGA and providing additional functionality then BIOS update would be >>> required to describe all these >> >> The FPGA is on a PCIe card. PCIe cards are autodetected and not hardcoded in >> the BIOS table. > > Can we detect the devices on the FPGA as well, my guess is No. > And isn't the BIOS updated for FPGAs? BIOS tables are per board, same as DT > entries you would write for a card. This is not any different from any PCI(e) card with ASICs on it. You can't autodiscover what is on the PCI(e) card. The card has a vendor and device ID which are used to match a driver to the card and the driver knows what is on the card and writes the right registers, maps the interrupts and so on. > > Even for discoverable devices, DSDT provides methods to read data. > >> For this problem there are basically two approaches. >> >> 1) Extend all used drivers for the used peripherals with platform data >> support. Then write a PCIe driver which instantiates all the drivers for the >> peripherals found on the board and in the FPGA using platform devices and >> platform data. > > The problem with platform devices is that they require pdata and I do not > see a scalable way to do pdata > >> 2) Use DT overlays. This does not require any changes to any of the existing >> peripheral drivers already supporting DT. The way this works is you create a >> DT snippet that describes the peripherals on your PCIe card and then write a >> simple PCIe driver that loads the DT blob for said snippet when the card is >> detected. >> >> This does not yet work in the upstream kernel, but it is the preferred >> approach and multiple people are working on getting a solution for this >> upstream. E.g. see https://github.com/mfornero/linux/commits/dtbo_wip > > OTOH that does sounds bit better. But this also seems like shoving DT on > x86, akin to someone forcing you to use ACPI as they have toolsets and > prefer to use that. ACPI is used for the description provided by the bios, this is a description that is embedded within the kernel and specific to a particular driver, using ACPI just makes it more complicated. > > Finally as long as data is being discovered and not hard coded in kernel, I > really don't mind either way! It just means to an end! Well, which devices will be instantiated for a specific PCIe ID is still hardcoded in the kernel. But rather than having a C file which registers platform devices you have a device-tree which registers platform devices. -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
