The processor manual prescribes to clear reset of LVDS interface in CPG/MSSR module before display on, and to assert the same reset line at display off time, to have the module resuming in a known state.
The module is said to be in "standby state" at initialization time, and this requires, according to section 37.3.7 of the manual, to de-assert the reset to have it functional. Based on the original patch from Koji Matsuoka <koji.matsuoka...@renesas.com> Signed-off-by: Jacopo Mondi <jacopo+rene...@jmondi.org> --- This patch upports commit: https://git.kernel.org/pub/scm/linux/kernel/git/horms/renesas-bsp.git/commit/ ?id=23b62b82a5a705d28ddac1d973ee98e6f51d54ea Even without this patch the LVDS interface has been succesfully tested on V3M/Eagle boards, and this makes me wonder on the real need for reset to be handled by the driver. I've been able to 'test' the reset assertion/deassertion on Draak, whose LVDS interface is not yet being enabled due to missing LVDS PLL support. If someone with a V3M/Eagle could test this to make sure this doesn't break anything, we can then discuss on the real need for this patch to be mainlined. Also, a series of patches to add reset to R8A7795/R8A7796/R8A77965 LVDS device nodes will be upported if this patch is considered useful. For the interested ones (Laurent, Geert) reset de-assertion at display on time takes in average a hundreds of micro seconds. Thanks j --- drivers/gpu/drm/rcar-du/rcar_lvds.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/drivers/gpu/drm/rcar-du/rcar_lvds.c b/drivers/gpu/drm/rcar-du/rcar_lvds.c index 20e8c34..acf4238 100644 --- a/drivers/gpu/drm/rcar-du/rcar_lvds.c +++ b/drivers/gpu/drm/rcar-du/rcar_lvds.c @@ -14,6 +14,7 @@ #include <linux/of_device.h> #include <linux/of_graph.h> #include <linux/platform_device.h> +#include <linux/reset.h> #include <linux/slab.h> #include <drm/drm_atomic.h> @@ -53,6 +54,7 @@ struct rcar_lvds { void __iomem *mmio; struct clk *clock; + struct reset_control *rst; bool enabled; struct drm_display_mode display_mode; @@ -175,6 +177,12 @@ static void rcar_lvds_enable(struct drm_bridge *bridge) if (ret < 0) return; + ret = reset_control_deassert(lvds->rst); + if (ret < 0) { + clk_disable_unprepare(lvds->clock); + return; + } + /* * Hardcode the channels and control signals routing for now. * @@ -265,6 +273,7 @@ static void rcar_lvds_disable(struct drm_bridge *bridge) rcar_lvds_write(lvds, LVDCR0, 0); rcar_lvds_write(lvds, LVDCR1, 0); + reset_control_assert(lvds->rst); clk_disable_unprepare(lvds->clock); lvds->enabled = false; @@ -481,6 +490,12 @@ static int rcar_lvds_probe(struct platform_device *pdev) return PTR_ERR(lvds->clock); } + lvds->rst = devm_reset_control_get_optional_exclusive(&pdev->dev, NULL); + if (IS_ERR(lvds->rst)) { + dev_err(&pdev->dev, "failed to get reset\n"); + return PTR_ERR(lvds->rst); + } + drm_bridge_add(&lvds->bridge); return 0; -- 2.7.4
