lkml.org 
[lkml]   [2017]   [Aug]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    SubjectRe: [PATCH 3/3] dmaengine: sun6i: Add support for Allwinner A64
    Date
    On Freitag, 1. September 2017 02:31:35 CEST Andre Przywara wrote:
    > Hi,
    >
    > On 31/08/17 00:36, Stefan Brüns wrote:
    > > The A64 SoC has the same dma engine as the H3 (sun8i), with a
    > > reduced amount of physical channels. Add the proper config data
    > > and compatible string to support it.
    >
    > ...
    >
    > > diff --git a/drivers/dma/sun6i-dma.c b/drivers/dma/sun6i-dma.c
    > > index 5f4eee4513e5..6a17c5d63582 100644
    > > --- a/drivers/dma/sun6i-dma.c
    > > +++ b/drivers/dma/sun6i-dma.c
    > > @@ -1068,6 +1068,12 @@ static struct sun6i_dma_config sun8i_h3_dma_cfg = {
    > >
    > > .nr_max_vchans = 34,
    > > .dmac_variant = DMAC_VARIANT_H3,
    > >
    > > };
    > >
    > > +
    > > +static struct sun6i_dma_config sun50i_a64_dma_cfg = {
    > > + .nr_max_channels = 8,
    > > + .nr_max_requests = 27,
    > > + .nr_max_vchans = 38,
    > > + .dmac_variant = DMAC_VARIANT_H3,
    > >
    > > };
    > >
    > > static const struct of_device_id sun6i_dma_match[] = {
    > >
    > > @@ -1075,6 +1081,7 @@ static const struct of_device_id sun6i_dma_match[] =
    > > {>
    > > { .compatible = "allwinner,sun8i-a23-dma", .data = &sun8i_a23_dma_cfg
    },
    > > { .compatible = "allwinner,sun8i-a83t-dma", .data = &sun8i_a83t_dma_cfg
    > > },
    > > { .compatible = "allwinner,sun8i-h3-dma", .data = &sun8i_h3_dma_cfg },
    > >
    > > + { .compatible = "allwinner,sun50i-a64-dma", .data = &sun50i_a64_dma_cfg
    > > },>
    > > { /* sentinel */ }
    > >
    > > };
    > > MODULE_DEVICE_TABLE(of, sun6i_dma_match);
    >
    > I was wondering if should use the opportunity to expose those values as
    > DT properties instead of hard-wiring them to a compatible string in the
    > driver every time we add support for a new SoC?
    > We could introduce a new compatible string (say: "allwinner,sunxi-dma"),
    > then describe properties for the number of channels and requests and
    > vchans and parse those from the DT at probe time.
    > With this we might be able to support future SoCs without Linux *driver*
    > changes, by just providing the right DT. This would have worked already
    > for instance for the A83T support, which just changed those values.
    >
    > For instance with this quick patch below (just compile tested, and without
    > your refactoring).
    > The DT node would then read something like:
    > dma: dma-controller@01c02000 {
    > compatible = "allwinner,sun50i-a64-dma",
    > "allwinner,sunxi-dma";
    > reg = <0x01c02000 0x1000>;
    > interrupts = <GIC_SPI 50 IRQ_TYPE_LEVEL_HIGH>;
    > clocks = <&ccu CLK_BUS_DMA>;
    > resets = <&ccu RST_BUS_DMA>;
    > #dma-cells = <1>;
    > allwinner,max_channels = <8>;
    > allwinner,max_requests = <27>;
    > allwinner,max_vchans = <38>;
    > };

    For these 3 properties it likely is a good idea, but we would IMHO still have
    to care for the differences in the register settings:

    - A31 does not have a clock autogating register
    - A23 and A83t does have one at offset 0x20
    - A64, H3, H5 and R40 have it at offset 0x28

    There are also the incompatibilities in the "DMA channel configuration
    register" (burst length; burst width; burst length field offset).

    We can either have 3 different compatible strings, or another property for the
    register model.

    For the aw,max_requests and aw,max_vchans, maybe a bitmask per direction is a
    better option - it can encode the allowed DRQ numbers much better (e.g. for
    H3, the highest source DRQ is 24). The DRQ field in the channel configuration
    register is 5 bits, so the hightest port/DRQ number is 31.

    For aw,max_channels my first thought is - why max? is it variable? is there a
    min_channels? My suggestion would be (in order of preference): "aw,channels",
    "aw,dma_channels", "aw,available_channels".

    Kind regards,

    Stefan

    --
    Stefan Brüns / Bergstraße 21 / 52062 Aachen
    home: +49 241 53809034 mobile: +49 151 50412019

    \
     
     \ /
      Last update: 2017-09-01 03:20    [W:4.405 / U:0.140 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site