Re: [PATCH v3 14/25] drm/sun4i: sun6i_mipi_dsi: Increase hfp packet overhead

Jagan Teki
2018-10-29T14:28:14Z

On Mon, Oct 29, 2018 at 2:58 PM Maxime Ripard <maxime.ripard@bootlin.com> wrote:
>
> On Fri, Oct 26, 2018 at 08:13:33PM +0530, Jagan Teki wrote:
> > Increase the hfp packet overhead with another 10 bytes, the extra
> > 10 bytes(which is hblk packet overhead) is adding for hfp packet
> > overhead since hfp depends on hblk.
> >
> > This is truely as per BSP code from BPI-M64-bsp.
> > The real computation from BSP is
> > (in drivers/video/sunxi/disp2/disp/de/lowlevel_sun50iw1/de_dsi.c)
> > dsi_hbp = (hbp-hspw)*dsi_pixel_bits[format]/8 - (4+2);
> > dsi_hact = x * dsi_pixel_bits[format]/8;
> > dsi_hblk = (ht-hspw)*dsi_pixel_bits[format]/8-(4+4+2);
> > dsi_hfp = dsi_hblk - (4+dsi_hact+2) - (4+dsi_hbp+2);
> >
> > Example,
> > u32 fmt = dsi_pixel_bits[format]/8;
> > => ((ht-hspw)*fmt - 10) - (6 + x * fmt) - (6 + (hbp-hspw)*fmt - 6)
> > => (ht - hspw - x - (hbp - hspw)) * fmt - 16
> > => (ht - x - hbp) * fmt - 16
> > => (ht - x - (timmings->hor_total_time - timmings->hor_front_porch - x)
> > * fmt - 16
> > => (timmings->hor_total_time - x - timmings->hor_total_time +
> > timmings->hor_front_porch + x) * fmt - 16
> > => timmings->hor_front_porch * fmt - 16
> >
> > So, increase the DSI hfp packet overhead by hblk packet overhead.
> >
> > Tested on 2-lane, 4-lane MIPI-DSI LCD panels.
> >
> > Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
> > Tested-by: Jagan Teki <jagan@amarulasolutions.com>
> > ---
> > Changes for v3:
> > - new patch
> > Changes for v2:
> > - none
> >
> > drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 22 +++++++++++++---------
> > 1 file changed, 13 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > index 6584b51736a9..20e330186b7f 100644
> > --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > @@ -461,7 +461,7 @@ static void sun6i_dsi_setup_timings(struct sun6i_dsi *dsi,
> > {
> > struct mipi_dsi_device *device = dsi->device;
> > unsigned int Bpp = mipi_dsi_pixel_format_to_bpp(device->format) / 8;
> > - u16 hbp, hfp, hsa, hblk_max, hblk, vblk;
> > + u16 hbp, hfp_pkt_overhead, hfp, hsa, hblk_max, hblk, vblk;
> > size_t bytes;
> > u8 *buffer;
> >
> > @@ -484,14 +484,6 @@ static void sun6i_dsi_setup_timings(struct sun6i_dsi *dsi,
> > hbp = max((unsigned int)HBP_PACKET_OVERHEAD,
> > (mode->htotal - mode->hsync_end) * Bpp - HBP_PACKET_OVERHEAD);
> >
> > - /*
> > - * The frontporch is set using a blanking packet (4 bytes +
> > - * payload + 2 bytes). Its minimal size is therefore 6 bytes
> > - */
> > -#define HFP_PACKET_OVERHEAD 6
> > - hfp = max((unsigned int)HFP_PACKET_OVERHEAD,
> > - (mode->hsync_start - mode->hdisplay) * Bpp - HFP_PACKET_OVERHEAD);
> > -
> > /*
> > * hblk seems to be the line + porches length.
> > * The blank is set using a blanking packet (4 bytes + 4 bytes +
> > @@ -502,6 +494,18 @@ static void sun6i_dsi_setup_timings(struct sun6i_dsi *dsi,
> > hblk_max -= HBLK_PACKET_OVERHEAD;
> > hblk = max((unsigned int)HBLK_PACKET_OVERHEAD, hblk_max);
> >
> > + /*
> > + * The frontporch is set using a blanking packet (4 bytes +
> > + * payload + 2 bytes). Its minimal size is therefore 6 bytes
> > + *
> > + * According to BSP code, extra 10 bytes(which is hblk packet overhead)
> > + * is adding for hfp packet overhead since hfp depends on hblk.
>
> "According to the BSP code, another 10 bytes (the HBLK packet
> overhead) need to be added to the front porch overhead."
>
> How has this been verified? Since we have registers to set all the
> parameters, this seems kind of weird.

Verified based on the BSP calculation which I explained in commit
message and tested by validating these numbers with mainline vs bsp
code.