tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
drm/pl111: Support grayscale
Migrating the TI nspire calculators to use the PL111 driver for
framebuffer requires grayscale support for the elder panel
which uses 8bit grayscale only.
DRM does not support 8bit grayscale framebuffers in memory,
but by defining the bus format to be MEDIA_BUS_FMT_Y8_1X8 we
can get the hardware to turn on a grayscaling feature and
convert the RGB framebuffer to grayscale for us.
Cc: Daniel Tang <dt.tangr@gmail.com>
Cc: Fabian Vogt <fabian@ritter-vogt.de>
Tested-by: Fabian Vogt <fabian@ritter-vogt.de>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190805085847.25554-2-linus.walleij@linaro.org
+28
-2
+27
-2
drivers/gpu/drm/pl111/pl111_display.c
+27
-2
drivers/gpu/drm/pl111/pl111_display.c
···
128
128
struct drm_framebuffer *fb = plane->state->fb;
129
129
struct drm_connector *connector = priv->connector;
130
130
struct drm_bridge *bridge = priv->bridge;
131
+
bool grayscale = false;
131
132
u32 cntl;
132
133
u32 ppl, hsw, hfp, hbp;
133
134
u32 lpp, vsw, vfp, vbp;
···
188
187
if (connector->display_info.bus_flags &
189
188
DRM_BUS_FLAG_PIXDATA_DRIVE_NEGEDGE)
190
189
tim2 |= TIM2_IPC;
190
+
191
+
if (connector->display_info.num_bus_formats == 1 &&
192
+
connector->display_info.bus_formats[0] ==
193
+
MEDIA_BUS_FMT_Y8_1X8)
194
+
grayscale = true;
195
+
196
+
/*
197
+
* The AC pin bias frequency is set to max count when using
198
+
* grayscale so at least once in a while we will reverse
199
+
* polarity and get rid of any DC built up that could
200
+
* damage the display.
201
+
*/
202
+
if (grayscale)
203
+
tim2 |= TIM2_ACB_MASK;
191
204
}
192
205
193
206
if (bridge) {
···
233
218
234
219
writel(0, priv->regs + CLCD_TIM3);
235
220
236
-
/* Hard-code TFT panel */
237
-
cntl = CNTL_LCDEN | CNTL_LCDTFT | CNTL_LCDVCOMP(1);
221
+
/*
222
+
* Detect grayscale bus format. We do not support a grayscale mode
223
+
* toward userspace, instead we expose an RGB24 buffer and then the
224
+
* hardware will activate its grayscaler to convert to the grayscale
225
+
* format.
226
+
*/
227
+
if (grayscale)
228
+
cntl = CNTL_LCDEN | CNTL_LCDMONO8;
229
+
else
230
+
/* Else we assume TFT display */
231
+
cntl = CNTL_LCDEN | CNTL_LCDTFT | CNTL_LCDVCOMP(1);
232
+
238
233
/* On the ST Micro variant, assume all 24 bits are connected */
239
234
if (priv->variant->st_bitmux_control)
240
235
cntl |= CNTL_ST_CDWID_24;