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From:   Jagan Teki <jagan@amarulasolutions.com>
To:     Michael Turquette <mturquette@baylibre.com>,
        Stephen Boyd <sboyd@kernel.org>,
        Heiko Stuebner <heiko@sntech.de>
Cc:     linux-clk@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-rockchip@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-amarula <linux-amarula@amarulasolutions.com>,
        Jagan Teki <jagan@amarulasolutions.com>,
        Finley Xiao <finley.xiao@rock-chips.com>
Subject: [PATCH] clk: rockchip: Fix overflow rate during fractional approximation
Date:   Mon, 31 Aug 2020 21:44:36 +0530
Message-Id: <20200831161436.134186-1-jagan@amarulasolutions.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

The current rockchip fractional approximation overflow the desired
rate if parent rate is lower than the (rate * 20) for few clocks like
dclk_vopb_frac.

The overflow condition has observed in px30 for dclk_vopb_frac
clock with an input rate of 71.1MHz and parent rate of 24MHz is,

[    2.543280] rockchip-drm display-subsystem: bound ff460000.vop (ops vop_component_ops)
[    2.557313] rockchip-drm display-subsystem: bound ff470000.vop (ops vop_component_ops)
[    2.566356] rockchip-drm display-subsystem: bound ff140000.syscon:lvds (ops rockchip_lvds_component_ops)
[    2.576999] [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
[    2.592177] Unexpected kernel BRK exception at EL1
[    2.597551] Internal error: ptrace BRK handler: f20003e8 [#1] PREEMPT SMP
[    2.605143] Modules linked in:
[    2.608566] CPU: 1 PID: 31 Comm: kworker/1:1 Tainted: G     U            5.8.0-rc1-15632-g97edd822b844 #30
[    2.619363] Hardware name: Engicam PX30.Core C.TOUCH 2.0 10.1" Open Frame (DT)
[    2.627460] Workqueue: events deferred_probe_work_func
[    2.633209] pstate: 20000005 (nzCv daif -PAN -UAO BTYPE=--)
[    2.639445] pc : rational_best_approximation+0xc4/0xd0
[    2.645194] lr : rockchip_fractional_approximation+0xa8/0xe0
[    2.651520] sp : ffff800011ea31c0
[    2.655222] x29: ffff800011ea31c0 x28: ffff00007a4ecd50
[    2.661162] x27: ffff00007d042600 x26: 000000000439fca3
[    2.667102] x25: 0000000000000000 x24: ffff800011ac9948
[    2.673033] x23: ffff800011ea3308 x22: ffff00007d042418
[    2.678973] x21: ffff800011ea3240 x20: ffff800011ea3238
[    2.684904] x19: ea47000000000000 x18: 0000000000000000
[    2.690836] x17: 0000000000000500 x16: 0000000000000001
[    2.696775] x15: ffffffffffffffff x14: 0000000000000000
[    2.702707] x13: 0000000000000000 x12: 0000003c00000000
[    2.708647] x11: 0000000000000030 x10: 0101010101010101
[    2.714586] x9 : 0000032000000320 x8 : 7f7f7f7f7f7f7f7f
[    2.720517] x7 : 000000a3c59050d3 x6 : 0000000000000030
[    2.726457] x5 : ffff800011ea3240 x4 : ffff800011ea3238
[    2.732397] x3 : 000000000000ffff x2 : 000000000000ffff
[    2.738329] x1 : 00000000016e3600 x0 : 0000000001497e00
[    2.744269] Call trace:
[    2.747005]  rational_best_approximation+0xc4/0xd0
[    2.752365]  clk_fd_round_rate+0x8c/0x110
[    2.756846]  clk_composite_round_rate+0x30/0x40
[    2.761917]  clk_core_determine_round_nolock.part.30+0x44/0x80
[    2.768442]  clk_core_round_rate_nolock+0x78/0x80
[    2.773701]  clk_mux_determine_rate_flags+0xd8/0x200
[    2.779253]  clk_mux_determine_rate+0x10/0x20
[    2.784124]  clk_core_determine_round_nolock.part.30+0x1c/0x80
[    2.790639]  clk_core_round_rate_nolock+0x78/0x80
[    2.795900]  clk_core_round_rate_nolock+0x5c/0x80
[    2.801159]  clk_round_rate+0x64/0xf0
[    2.805254]  vop_crtc_mode_fixup+0x2c/0x60
[    2.809828]  drm_atomic_helper_check_modeset+0x95c/0xae0
[    2.815767]  drm_atomic_helper_check+0x1c/0xa0
[    2.820738]  drm_atomic_check_only+0x43c/0x760
[    2.825705]  drm_atomic_commit+0x18/0x60
[    2.830095]  drm_client_modeset_commit_atomic.isra.16+0x17c/0x250
[    2.836911]  drm_client_modeset_commit_locked+0x58/0x1a0
[    2.842851]  drm_client_modeset_commit+0x2c/0x50
[    2.848014]  drm_fb_helper_restore_fbdev_mode_unlocked+0x70/0xd0
[    2.854730]  drm_fb_helper_set_par+0x2c/0x60
[    2.859497]  fbcon_init+0x3c0/0x540
[    2.863400]  visual_init+0xac/0x100
[    2.867298]  do_bind_con_driver+0x1e4/0x3a0
[    2.871973]  do_take_over_console+0x140/0x200
[    2.876843]  do_fbcon_takeover+0x6c/0xe0
[    2.881228]  fbcon_fb_registered+0x10c/0x120
[    2.886005]  register_framebuffer+0x1f0/0x340
[    2.890878]  __drm_fb_helper_initial_config_and_unlock+0x318/0x4a0
[    2.897790]  drm_fb_helper_initial_config+0x3c/0x50
[    2.903244]  rockchip_drm_fbdev_init+0x5c/0xf0
[    2.908202]  rockchip_drm_bind+0x194/0x1e0
[    2.912785]  try_to_bring_up_master+0x164/0x1d0
[    2.917851]  component_master_add_with_match+0xac/0xf0
[    2.923597]  rockchip_drm_platform_probe+0x238/0x2e0
[    2.929150]  platform_drv_probe+0x50/0xa0
[    2.933631]  really_probe+0xd4/0x330
[    2.937628]  driver_probe_device+0x54/0xb0
[    2.942207]  __device_attach_driver+0x80/0xc0
[    2.947078]  bus_for_each_drv+0x78/0xd0
[    2.951365]  __device_attach+0xd4/0x130
[    2.955652]  device_initial_probe+0x10/0x20
[    2.960328]  bus_probe_device+0x90/0xa0
[    2.964616]  deferred_probe_work_func+0x6c/0xa0
[    2.969685]  process_one_work+0x1e4/0x360
[    2.974166]  worker_thread+0x208/0x480
[    2.978358]  kthread+0x150/0x160
[    2.981968]  ret_from_fork+0x10/0x18
[    2.985970] Code: d65f03c0 d2800008 d2800027 17ffffe8 (d4207d00)

This happened because the fractional divider does not apply if parent_rate
is lower than (rate * 20).

So, this patch is trying to fix that overflow clock and switch to half-div
instead computing fractioanl approximation.

Some part of the patch is referenced from below BSP commit:

commit <88a5404a2277> ("clk: rockchip: fix up the
rockchip_fractional_approximation")

commit <4186a0e4239b> ("clk: rockchip: Add supprot to limit input rate
for fractional divider")

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Signed-off-by: Finley Xiao <finley.xiao@rock-chips.com>
---
 drivers/clk/rockchip/clk-px30.c | 12 ++++++------
 drivers/clk/rockchip/clk.c      |  9 +++++++++
 2 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/drivers/clk/rockchip/clk-px30.c b/drivers/clk/rockchip/clk-px30.c
index 6fb9c98b7d24..06d3ff39d12f 100644
--- a/drivers/clk/rockchip/clk-px30.c
+++ b/drivers/clk/rockchip/clk-px30.c
@@ -660,7 +660,7 @@ static struct rockchip_clk_branch px30_clk_branches[] __initdata = {
 	COMPOSITE(SCLK_UART1_SRC, "clk_uart1_src", mux_uart_src_p, CLK_SET_RATE_NO_REPARENT,
 			PX30_CLKSEL_CON(34), 14, 2, MFLAGS, 0, 5, DFLAGS,
 			PX30_CLKGATE_CON(10), 12, GFLAGS),
-	COMPOSITE_NOMUX_HALFDIV(0, "clk_uart1_np5", "clk_uart1_src", 0,
+	COMPOSITE_NOMUX_HALFDIV(0, "clk_uart1_np5", "clk_uart1_src", CLK_SET_RATE_PARENT,
 			PX30_CLKSEL_CON(35), 0, 5, DFLAGS,
 			PX30_CLKGATE_CON(10), 13, GFLAGS),
 	COMPOSITE_FRACMUX(0, "clk_uart1_frac", "clk_uart1_src", CLK_SET_RATE_PARENT,
@@ -673,7 +673,7 @@ static struct rockchip_clk_branch px30_clk_branches[] __initdata = {
 	COMPOSITE(SCLK_UART2_SRC, "clk_uart2_src", mux_uart_src_p, 0,
 			PX30_CLKSEL_CON(37), 14, 2, MFLAGS, 0, 5, DFLAGS,
 			PX30_CLKGATE_CON(11), 0, GFLAGS),
-	COMPOSITE_NOMUX_HALFDIV(0, "clk_uart2_np5", "clk_uart2_src", 0,
+	COMPOSITE_NOMUX_HALFDIV(0, "clk_uart2_np5", "clk_uart2_src", CLK_SET_RATE_PARENT,
 			PX30_CLKSEL_CON(38), 0, 5, DFLAGS,
 			PX30_CLKGATE_CON(11), 1, GFLAGS),
 	COMPOSITE_FRACMUX(0, "clk_uart2_frac", "clk_uart2_src", CLK_SET_RATE_PARENT,
@@ -686,7 +686,7 @@ static struct rockchip_clk_branch px30_clk_branches[] __initdata = {
 	COMPOSITE(0, "clk_uart3_src", mux_uart_src_p, 0,
 			PX30_CLKSEL_CON(40), 14, 2, MFLAGS, 0, 5, DFLAGS,
 			PX30_CLKGATE_CON(11), 4, GFLAGS),
-	COMPOSITE_NOMUX_HALFDIV(0, "clk_uart3_np5", "clk_uart3_src", 0,
+	COMPOSITE_NOMUX_HALFDIV(0, "clk_uart3_np5", "clk_uart3_src", CLK_SET_RATE_PARENT,
 			PX30_CLKSEL_CON(41), 0, 5, DFLAGS,
 			PX30_CLKGATE_CON(11), 5, GFLAGS),
 	COMPOSITE_FRACMUX(0, "clk_uart3_frac", "clk_uart3_src", CLK_SET_RATE_PARENT,
@@ -699,7 +699,7 @@ static struct rockchip_clk_branch px30_clk_branches[] __initdata = {
 	COMPOSITE(0, "clk_uart4_src", mux_uart_src_p, 0,
 			PX30_CLKSEL_CON(43), 14, 2, MFLAGS, 0, 5, DFLAGS,
 			PX30_CLKGATE_CON(11), 8, GFLAGS),
-	COMPOSITE_NOMUX_HALFDIV(0, "clk_uart4_np5", "clk_uart4_src", 0,
+	COMPOSITE_NOMUX_HALFDIV(0, "clk_uart4_np5", "clk_uart4_src", CLK_SET_RATE_PARENT,
 			PX30_CLKSEL_CON(44), 0, 5, DFLAGS,
 			PX30_CLKGATE_CON(11), 9, GFLAGS),
 	COMPOSITE_FRACMUX(0, "clk_uart4_frac", "clk_uart4_src", CLK_SET_RATE_PARENT,
@@ -712,7 +712,7 @@ static struct rockchip_clk_branch px30_clk_branches[] __initdata = {
 	COMPOSITE(0, "clk_uart5_src", mux_uart_src_p, 0,
 			PX30_CLKSEL_CON(46), 14, 2, MFLAGS, 0, 5, DFLAGS,
 			PX30_CLKGATE_CON(11), 12, GFLAGS),
-	COMPOSITE_NOMUX_HALFDIV(0, "clk_uart5_np5", "clk_uart5_src", 0,
+	COMPOSITE_NOMUX_HALFDIV(0, "clk_uart5_np5", "clk_uart5_src", CLK_SET_RATE_PARENT,
 			PX30_CLKSEL_CON(47), 0, 5, DFLAGS,
 			PX30_CLKGATE_CON(11), 13, GFLAGS),
 	COMPOSITE_FRACMUX(0, "clk_uart5_frac", "clk_uart5_src", CLK_SET_RATE_PARENT,
@@ -934,7 +934,7 @@ static struct rockchip_clk_branch px30_clk_pmu_branches[] __initdata = {
 	COMPOSITE(0, "clk_uart0_pmu_src", mux_uart_src_p, 0,
 			PX30_PMU_CLKSEL_CON(3), 14, 2, MFLAGS, 0, 5, DFLAGS,
 			PX30_PMU_CLKGATE_CON(1), 0, GFLAGS),
-	COMPOSITE_NOMUX_HALFDIV(0, "clk_uart0_np5", "clk_uart0_pmu_src", 0,
+	COMPOSITE_NOMUX_HALFDIV(0, "clk_uart0_np5", "clk_uart0_pmu_src", CLK_SET_RATE_PARENT,
 			PX30_PMU_CLKSEL_CON(4), 0, 5, DFLAGS,
 			PX30_PMU_CLKGATE_CON(1), 1, GFLAGS),
 	COMPOSITE_FRACMUX(0, "clk_uart0_frac", "clk_uart0_pmu_src", CLK_SET_RATE_PARENT,
diff --git a/drivers/clk/rockchip/clk.c b/drivers/clk/rockchip/clk.c
index 546e810c3560..38d032faa05e 100644
--- a/drivers/clk/rockchip/clk.c
+++ b/drivers/clk/rockchip/clk.c
@@ -190,6 +190,15 @@ static void rockchip_fractional_approximation(struct clk_hw *hw,
 		p_parent = clk_hw_get_parent(clk_hw_get_parent(hw));
 		p_parent_rate = clk_hw_get_rate(p_parent);
 		*parent_rate = p_parent_rate;
+
+		/* fractional divider not apply if parent_rate is lower than (rate * 20) */
+		if (*parent_rate < rate * 20) {
+			pr_warn("%s: %s fractional div is not allowed, so use half-div\n",
+				__func__, clk_hw_get_name(hw));
+			*m = 0;
+			*n = 1;
+			return;
+		}
 	}
 
 	/*
-- 
2.25.1