linux-kernel - Re: [PATCH v2 06/15] drm/mxsfb: Update mxsfb with additional pixel formats

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Date:   Wed, 14 Aug 2019 12:44:34 +0100
From:   Daniel Stone <daniel@...ishbar.org>
To:     Robert Chiras <robert.chiras@....com>
Cc:     Guido Günther <agx@...xcpu.org>,
        Marek Vasut <marex@...x.de>, Stefan Agner <stefan@...er.ch>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        NXP Linux Team <linux-imx@....com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 06/15] drm/mxsfb: Update mxsfb with additional pixel formats

Hi Robert,

On Wed, 14 Aug 2019 at 11:49, Robert Chiras <robert.chiras@....com> wrote:
> +       case DRM_FORMAT_BGR565: /* BG16 */
> +               if (mxsfb->devdata->ipversion < 4)
> +                       goto err;
> +               writel(CTRL2_ODD_LINE_PATTERN(CTRL2_LINE_PATTERN_BGR) |
> +                       CTRL2_EVEN_LINE_PATTERN(CTRL2_LINE_PATTERN_BGR),
> +                       mxsfb->base + LCDC_V4_CTRL2 + REG_SET);
> +               /* Fall through */
> +       case DRM_FORMAT_RGB565: /* RG16 */
> +               ctrl |= CTRL_SET_WORD_LENGTH(0);
> +               ctrl &= ~CTRL_DF16;
> +               ctrl1 |= CTRL1_SET_BYTE_PACKAGING(0xf);
> +               break;

For non-BGR formats, do you need to write RGB line-pattern back to the
CTRL2 register? Otherwise, if you start with BGR565 then switch back
to RGB565, presumably CTRL2 would still be programmed for BGR so you
would display inverted channels.

Same goes for all the other BGR/RGB format pairs below.

Cheers,
Daniel