linux-kernel - Re: [PATCH v3 2/4] arm64: dts: sc7180: Specify "data-lanes" for DSI host output

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Date:   Mon, 1 Nov 2021 09:39:20 -0700
From:   Philip Chen <philipchen@...omium.org>
To:     Abhinav Kumar <quic_abhinavk@...cinc.com>
Cc:     Stephen Boyd <swboyd@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>, dianders@...omium.org,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v3 2/4] arm64: dts: sc7180: Specify "data-lanes" for DSI
 host output

Hi,

On Sun, Oct 31, 2021 at 7:52 PM Abhinav Kumar <quic_abhinavk@...cinc.com> wrote:
>
>
> On 10/31/2021 2:01 PM, Abhinav Kumar wrote:
>
> Hi Philip
>
> On 10/29/2021 4:24 PM, Philip Chen wrote:
>
> Hi Stephen,
>
> On Fri, Oct 29, 2021 at 4:16 PM Stephen Boyd <swboyd@...omium.org> wrote:
>
> Quoting Philip Chen (2021-10-29 15:27:41)
>
> MSM DSI host driver actually parses "data-lanes" in DT and compare
> it with the number of DSI lanes the bridge driver sets for
> mipi_dsi_device. So we need to always specify "data-lanes" for the
> DSI host output. As of now, "data-lanes" is added to ti-sn65dsi86 dts
> fragment, but missing in parade-ps8640 dts fragment, which requires
> a fixup.
>
> I don't see data-lanes required in the schema, and
> dsi_host_parse_lane_data() seems happy to continue without it. I do see
> that num_data_lanes isn't set though. Does this patch fix it?
>
> The problem I see is from dsi_host_attach().
> If there is no "data-lanes" in DT, num_data_lanes would be 0.
> Then dsi_host_attach() would return -EINVAL.
>
> Let me know if i am missing something here. the dsi_host_attach returns an error if
>
> dsi->lanes is > than msm_host->num_data_lanes. That shouldnt happen even if
>
> num_data_lanes will be 0
>
> static int dsi_host_attach(struct mipi_dsi_host *host,
>                     struct mipi_dsi_device *dsi)
> {
>     struct msm_dsi_host *msm_host = to_msm_dsi_host(host);
>     int ret;
>
>     if (dsi->lanes > msm_host->num_data_lanes)
>         return -EINVAL;
>
> Thanks
>
> Abhinav
>
> Please ignore this comment, I understood now. The fix you had posted to default to 4 lanes seems fine.
>
> Will ack that one.
Thanks!
For the other folks: the fix I posted for dsi_host is here:
https://patchwork.kernel.org/project/linux-arm-msm/patch/20211030100812.1.I6cd9af36b723fed277d34539d3b2ba4ca233ad2d@changeid/

>
>
> ----8<----
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c
> b/drivers/gpu/drm/msm/dsi/dsi_host.c
> index e269df285136..f6fba07220e5 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> @@ -1696,6 +1696,7 @@ static int dsi_host_parse_lane_data(struct
> msm_dsi_host *msm_host,
>         if (!prop) {
>                 DRM_DEV_DEBUG(dev,
>                         "failed to find data lane mapping, using default\n");
> +               msm_host->num_data_lanes = 4;
>                 return 0;
>         }
>
> I haven't tried.
> But I think it can fix the problem I described above.
> Would you like to send it as a separate patch?
> Or I can do it.