Re: [PATCH] drm/mxsfb: use bus_format to determine LCD bus width

From: Stefan Agner
Date: Thu Dec 08 2016 - 22:51:35 EST


On 2016-12-08 15:33, Marek Vasut wrote:
> On 12/08/2016 11:52 PM, Stefan Agner wrote:
>> The LCD bus width does not need to align with the pixel format. The
>> LCDIF controller automatically converts between pixel formats and
>> bus width by padding or dropping LSBs.
>>
>> The DRM subsystem has the notion of bus_format which allows to
>> determine what bus_formats are supported by the display. Choose the
>> first available or fallback to 24 bit if none are available.
>>
>> Signed-off-by: Stefan Agner <stefan@xxxxxxxx>
>> ---
>> drivers/gpu/drm/mxsfb/mxsfb_crtc.c | 28 +++++++++++++++++++++++++---
>> drivers/gpu/drm/mxsfb/mxsfb_regs.h | 1 +
>> 2 files changed, 26 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_crtc.c b/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
>> index 4bcc8a3..00fa244 100644
>> --- a/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
>> +++ b/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
>> @@ -65,13 +65,11 @@ static int mxsfb_set_pixel_fmt(struct mxsfb_drm_private *mxsfb)
>
> You should probably drop the WARNING: comment in this function too.
>
>> switch (format) {
>> case DRM_FORMAT_RGB565:
>> dev_dbg(drm->dev, "Setting up RGB565 mode\n");
>> - ctrl |= CTRL_SET_BUS_WIDTH(STMLCDIF_16BIT);
>> ctrl |= CTRL_SET_WORD_LENGTH(0);
>> ctrl1 |= CTRL1_SET_BYTE_PACKAGING(0xf);
>> break;
>> case DRM_FORMAT_XRGB8888:
>> dev_dbg(drm->dev, "Setting up XRGB8888 mode\n");
>> - ctrl |= CTRL_SET_BUS_WIDTH(STMLCDIF_24BIT);
>> ctrl |= CTRL_SET_WORD_LENGTH(3);
>> /* Do not use packed pixels = one pixel per word instead. */
>> ctrl1 |= CTRL1_SET_BYTE_PACKAGING(0x7);
>> @@ -89,6 +87,9 @@ static int mxsfb_set_pixel_fmt(struct mxsfb_drm_private *mxsfb)
>>
>> static void mxsfb_enable_controller(struct mxsfb_drm_private *mxsfb)
>> {
>> + struct drm_crtc *crtc = &mxsfb->pipe.crtc;
>> + struct drm_device *drm = crtc->dev;
>> + u32 bus_format = MEDIA_BUS_FMT_RGB888_1X24;
>
> So why do you move the bus width configuration from
> mxsfb_set_pixel_fmt() to here ? Is there any reason
> for it?
>

To emphasize that it is not related to pixel format. Also, if you have a
controller with multiple framebuffers/layers, mxsfb_set_pixel_fmt would
get called per layer...

In a full DRM driver it probably would be part of a encoder function, I
feel here it seems to map best to enable controller. It could probably
also be in mxsfb_crtc_enable (or even mxsfb_crtc_mode_set_nofb I guess),
but we do not touch LCDC_CTRL there...

>> u32 reg;
>>
>> if (mxsfb->clk_disp_axi)
>> @@ -97,7 +98,28 @@ static void mxsfb_enable_controller(struct mxsfb_drm_private *mxsfb)
>> mxsfb_enable_axi_clk(mxsfb);
>>
>> /* If it was disabled, re-enable the mode again */
>> - writel(CTRL_DOTCLK_MODE, mxsfb->base + LCDC_CTRL + REG_SET);
>> + reg = readl(mxsfb->base + LCDC_CTRL);
>
> Wouldn't it make more sense to cache the LCDC_CTRL content rather than
> doing R-M-W on it ?
>

Not sure what you mean by cache? Isn't the variable reg counting as a
cache?

>> + reg |= CTRL_DOTCLK_MODE;
>> +
>> + if (mxsfb->connector.display_info.num_bus_formats)
>> + bus_format = mxsfb->connector.display_info.bus_formats[0];
>> +
>> + reg &= ~CTRL_BUS_WIDTH_MASK;
>> + switch (bus_format) {
>> + case MEDIA_BUS_FMT_RGB565_1X16:
>> + reg |= CTRL_SET_BUS_WIDTH(STMLCDIF_16BIT);
>> + break;
>> + case MEDIA_BUS_FMT_RGB666_1X18:
>> + reg |= CTRL_SET_BUS_WIDTH(STMLCDIF_18BIT);
>> + break;
>> + case MEDIA_BUS_FMT_RGB888_1X24:
>> + reg |= CTRL_SET_BUS_WIDTH(STMLCDIF_24BIT);
>> + break;
>> + default:
>> + dev_err(drm->dev, "Unknown media bus format %d\n", bus_format);
>> + break;
>> + }
>> + writel(reg, mxsfb->base + LCDC_CTRL);
>
> On MX6SX:
> Tested-by: Marek Vasut <marex@xxxxxxx>

Thx!

--
Stefan