[U-Boot] [PATCH 3/4] pci: mediatek: Add pci-driver for mt2701

[Frank Wunderlich]

Hi Ryder,

you know that we cannot write a full, multi-device driver here :)

> Gesendet: Mittwoch, 31. Juli 2019 um 17:23 Uhr
> Von: "Ryder Lee" <ryder.lee at mediatek.com>
> > imho we can use single driver for different IP generation and that is
> > what we did in linux now.
> >
> > MT7623/MT2701 - mtk_pcie_soc_v1
> > MT7622/MT7629 - v2
> > gen3 IP - TBD

i ack that's the right way, but this cannot be done by people outside (that do not have knowledge about multiple chips the driver should cover) and not only in freetime, so our approach was to create a driver for this chip (that is also used by other soc) as base for future developement (extending for other boards).

on any time it needs to be replaced by a more universal variant to have not the same code multiple times. but thats far away from we can do here

it's not the best code (based on magic values and portability to other devices), but from my point of view we have working sata and do not modify existing code too much (to avoid side-effects), but only figuring out which consts are used in linux take much time for us

> > phy driver is used for configuring basic settings, there is no complex
> > logic in it. we can even copy and paste the entire block from that
> > driver.
you know the technical details :)
what we do is read out registers in linux and try to adapt this in uboot ;) because drivercode itself is too big for us to understand

> > .version = MTK_PHY_V1
> > case PHY_TYPE_PCIE:
> > 	pcie_phy_instance_init(tphy, instance);
> More specifically, we should use pci_generic_mmap_write/read_config()
> for standard set of confi read/write operations so that we can get rid
> of the helpers here.

a general way is right, but not possible to created by people not working for mtk :) without the right documentation

we do not have the knowledge to port a driver like this from linux to uboot

> I think the uboot driver end up dealing with nothing but just doing some
> initial parts (< 300 lines I guess), or you can take pcie_xilinx or
> pci_tegra as examples.
> > we can directly replace these chunks with mtk_pcie_startup_port()
> > (pcie-mediatek.c) and there are many defines for the registers/bit
> > field.

i tried this, but just C&P does not work ( i'm not that naive :) ) because of many depencies (functions used in linux-variant), i have already changed some things, but it ended in needed touching corefiles of uboot (e.g. extending pci.h) which may break other drivers.

but at least i have this version (with some fix-ups you've mentioned here) on my github-repo so that everybody can use it for my board/other boards using mt2701

https://github.com/frank-w/u-boot/commits/2019-07-bpi-r2-sata_new (will merge that in other main branches till official driver is there)

regards Frank