linux-kernel - Re: [PATCH v3 07/14] dt-bindings: dma: ti: Add document for K3 UDMA

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Date:   Thu, 17 Oct 2019 09:03:55 -0500
From:   Rob Herring <robh@...nel.org>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
Cc:     Nishanth Menon <nm@...com>, devicetree@...r.kernel.org,
        Grygorii Strashko <grygorii.strashko@...com>,
        Lokesh Vutla <lokeshvutla@...com>, Keerthy <j-keerthy@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Tero Kristo <t-kristo@...com>,
        Tony Lindgren <tony@...mide.com>, Vinod <vkoul@...nel.org>,
        Santosh Shilimkar <ssantosh@...nel.org>,
        "open list:DMA GENERIC OFFLOAD ENGINE SUBSYSTEM" 
        <dmaengine@...r.kernel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 07/14] dt-bindings: dma: ti: Add document for K3 UDMA

On Tue, Oct 15, 2019 at 12:29 PM Peter Ujfalusi <peter.ujfalusi@...com> wrote:
>
> Rob,
>
> On 10/11/19 10:30 AM, Peter Ujfalusi wrote:
> >
> > I have already moved the TR vs Packet mode channel selection, which does
> > make sense as it was Linux's choice to use TR for certain cases.
> >
> > If I move these to code then we need to have big tables
> > struct psil_config am654_psil[32767] = {};
> > struct psil_config j721e_psil[32767] = {};
>
> After thinking about this a bit more, I think we can move all the PSI-L
> endpoint configuration to the kernel as not all the 32767 threads are
> actually in use. Sure it is going to be some amount of static data in
> the kernel, but it is an acceptable compromise.
>
> The DMA binding can look like this:
>
> dmas = <&main_udmap 0xc400>,
>        <&main_udmap 0x4400>;
> dma-names = "tx", "rx";
>
> or
> dmas = <&main_udmap 0x4400 UDMA_DIR_TX>,
>        <&main_udmap 0x4400 UDMA_DIR_RX>;
> dma-names = "tx", "rx";
>
> If I keep the direction.
> 0xc400 is destination ID, which is 0x4400 | 0x8000 as per PSI-L
> specification.
> In the TRM only the source threads can be found as a map (thread IDs <
> 0x7fff), but the binding document can cover this.
>
> This way we don't need another dtsi file and I can create the map in the
> kernel.
>
> This will hide some details of the HW from DT, but since the PSI-L
> thread configuration is static in hardware I believe it is acceptable.
>
> However we still have uncovered features in the binding or in code, like
> a case when the RX does not have access to the DMA channel, only flows.
> Not sure if I should reserve the direction parameter as an indication to
> this or find other way.
> Basically we communicate on the given PSI-L thread without having a DMA
> channel as other core is owning the channel.
>
> What do you think?

Seems like a reasonable solution though I don't really follow the last issue.

Rob