From: Daniil Gnusarev <gnusarevda@basealt.ru> To: devel-kernel@lists.altlinux.org Subject: [d-kernel] [PATCH 28/39] serial: 8250_dw: verify clock rate in dw8250_set_termios Date: Mon, 14 Oct 2024 18:02:09 +0400 Message-ID: <20241014140221.535985-29-gnusarevda@basealt.ru> (raw) In-Reply-To: <20241014140221.535985-1-gnusarevda@basealt.ru> From: Alexey Sheplyakov <asheplyakov@basealt.ru> Refuse to change the clock rate if clk_round_rate() returns a rate which is way too off (i.e. by more than 1/16 from the one necessary for a given baud rate). In particular this happens if the requested rate is below the minimum supported by the clock. Fixes the UART console on Baikal-M SoC. Without this patch the console gets garbled immediately after loading the driver. dw8250_set_termios tries to configure the baud rate (115200), and calls clk_round_rate to figure out the supported rate closest to 1843200 Hz (which is 115200 * 16). However the (SoC-specific) clock driver returns 4705882 Hz. This frequency is way too off, hence after setting it the console gets garbled. On Baikal-M Linux has no direct control over (most) clocks. The registers of CMU (clock management unit) are accessible only from the secure world, therefore clocks are managed by the firmware (ARM-TF). Linux' driver, clk-baikal, is a shim which calls into firmware. And that 4705882 Hz is exactly what the firmware returns. According to 8250_dw maintainer (Andy Shevchenko) the correct way to fix the problem is to 1) use DLAB for the baud rate and fixed clock rate, 2) fix the firmware Neither of these advices can be applied in practice. For one, both methods require replacing the DTB, which is embedded into the firmware. Updating firmware is possible only for some types of (Baikal-M) based boards, and requires special hardware (JTAG programmer) and skills. Therfore the only practical way to address the issue is to adjust the kernel (with this ugly patch). Signed-off-by: Alexey Sheplyakov <asheplyakov@basealt.ru> Co-developed-by: Vadim V. Vlasov <vadim.vlasov@elpitech.ru> X-DONTUPSTREAM X-feature-Baikal-M --- drivers/tty/serial/8250/8250_dw.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c index 85b6294c87ba5..29bd35069cd3e 100644 --- a/drivers/tty/serial/8250/8250_dw.c +++ b/drivers/tty/serial/8250/8250_dw.c @@ -379,14 +379,15 @@ dw8250_do_pm(struct uart_port *port, unsigned int state, unsigned int old) static void dw8250_set_termios(struct uart_port *p, struct ktermios *termios, const struct ktermios *old) { - unsigned long newrate = tty_termios_baud_rate(termios) * 16; + unsigned long baud = tty_termios_baud_rate(termios); + unsigned long newrate = baud * 16; struct dw8250_data *d = to_dw8250_data(p->private_data); long rate; int ret; clk_disable_unprepare(d->clk); rate = clk_round_rate(d->clk, newrate); - if (rate > 0) { + if (rate > 0 && rate >= baud * 15 && rate <= baud * 17) { /* * Note that any clock-notifer worker will block in * serial8250_update_uartclk() until we are done. -- 2.42.2
next prev parent reply other threads:[~2024-10-14 14:02 UTC|newest] Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top 2024-10-14 14:01 [d-kernel] [PATCH 00/39] Support Baikal-M in un-def in p11 Daniil Gnusarev 2024-10-14 14:01 ` [d-kernel] [PATCH 01/39] Baikal Electronics SoC family Daniil Gnusarev 2024-10-14 14:01 ` [d-kernel] [PATCH 02/39] Clk: Add clock drivers for Baikal BE-M1000 with new firmware Daniil Gnusarev 2024-10-14 14:01 ` [d-kernel] [PATCH 03/39] USB: Add support for Baikal USB PHY Daniil Gnusarev 2024-10-14 14:01 ` [d-kernel] [PATCH 04/39] PCI: Add support for PCIe controller for Baikal BE-M1000 Daniil Gnusarev 2024-10-14 14:01 ` [d-kernel] [PATCH 05/39] AHCI SATA: Add support " Daniil Gnusarev 2024-10-14 14:01 ` [d-kernel] [PATCH 06/39] UART: Add support for UART " Daniil Gnusarev 2024-10-14 14:01 ` [d-kernel] [PATCH 07/39] cpufreq-dt: don't load on Baikal-M SoC Daniil Gnusarev 2024-10-14 14:01 ` [d-kernel] [PATCH 08/39] Sound: add support for Baikal BE-M1000 I2S Daniil Gnusarev 2024-10-14 14:01 ` [d-kernel] [PATCH 09/39] sound: baikal-i2s: paper over RX overrun warnings on Baikal-M Daniil Gnusarev 2024-10-14 14:01 ` [d-kernel] [PATCH 10/39] net: stmmac: support of Baikal-BE1000 SoCs GMAC Daniil Gnusarev 2024-10-14 14:01 ` [d-kernel] [PATCH 11/39] net: fwnode_get_phy_id: consider all compatible strings Daniil Gnusarev 2024-10-14 14:01 ` [d-kernel] [PATCH 12/39] hwmon: bt1-pvt: access registers via pvt_{readl, writel} helpers Daniil Gnusarev 2024-10-14 14:01 ` [d-kernel] [PATCH 13/39] hwmon: bt1-pvt: define pvt_readl/pvt_writel for Baikal-M SoC Daniil Gnusarev 2024-10-14 14:01 ` [d-kernel] [PATCH 14/39] hwmon: bt1-pvt: adjusted probing " Daniil Gnusarev 2024-10-14 14:01 ` [d-kernel] [PATCH 15/39] hwmon: bt1-pvt: added compatible baikal, pvt Daniil Gnusarev 2024-10-14 14:01 ` [d-kernel] [PATCH 16/39] PVT: support register addressing with new firmware Daniil Gnusarev 2024-10-14 14:01 ` [d-kernel] [PATCH 17/39] drm: add Baikal-M SoC video display unit driver Daniil Gnusarev 2024-10-14 14:01 ` [d-kernel] [PATCH 18/39] drm/bridge: dw-hdmi: support ahb audio hw revision 0x2a Daniil Gnusarev 2024-10-14 14:02 ` [d-kernel] [PATCH 19/39] dt-bindings: dw-hdmi: added ahb-audio-regshift Daniil Gnusarev 2024-10-14 14:02 ` [d-kernel] [PATCH 20/39] drm/bridge: dw-hdmi: force ahb audio register offset for Baikal-M Daniil Gnusarev 2024-10-14 14:02 ` [d-kernel] [PATCH 21/39] drm/panfrost: forcibly set dma-coherent on Baikal-M Daniil Gnusarev 2024-10-14 14:02 ` [d-kernel] [PATCH 22/39] drm/panfrost: disable devfreq " Daniil Gnusarev 2024-10-14 14:02 ` [d-kernel] [PATCH 23/39] bmc: add board management controller driver Daniil Gnusarev 2024-10-14 14:02 ` [d-kernel] [PATCH 24/39] pm: disable all sleep states on Baikal-M based boards Daniil Gnusarev 2024-10-14 14:02 ` [d-kernel] [PATCH 25/39] sound: dwc-i2s: paper over RX overrun warnings on Baikal-M Daniil Gnusarev 2024-10-14 14:02 ` [d-kernel] [PATCH 26/39] sound: dwc-i2s: request all IRQs specified in device tree Daniil Gnusarev 2024-10-14 14:02 ` [d-kernel] [PATCH 27/39] usb: dwc3: of-simple: added compatible string for Baikal-M SoC Daniil Gnusarev 2024-10-14 14:02 ` Daniil Gnusarev [this message] 2024-10-14 14:02 ` [d-kernel] [PATCH 29/39] clk: use "cmu-id" if there is no "reg" in devicetree Daniil Gnusarev 2024-10-14 14:02 ` [d-kernel] [PATCH 30/39] pci: baikal-pcie: driver compatibility with SDK earlier than 5.7 Daniil Gnusarev 2024-10-14 14:02 ` [d-kernel] [PATCH 31/39] pci: baikal-pcie: driver compatibility with SDK versions 5.4 Daniil Gnusarev 2024-10-14 14:02 ` [d-kernel] [PATCH 32/39] dw-pcie: refuse to load on Baikal-M with recent firmware Daniil Gnusarev 2024-10-14 14:02 ` [d-kernel] [PATCH 33/39] drm: baikal-vdu: driver compatibility with SDK earlier than 5.9 Daniil Gnusarev 2024-10-14 14:02 ` [d-kernel] [PATCH 34/39] input: new driver - serdev-serio Daniil Gnusarev 2024-10-14 14:02 ` [d-kernel] [PATCH 35/39] input: added TF307 serio PS/2 emulator driver Daniil Gnusarev 2024-10-14 14:02 ` [d-kernel] [PATCH 36/39] input: tp_serio: catch up API changes Daniil Gnusarev 2024-10-14 14:02 ` [d-kernel] [PATCH 37/39] drm: baikal-m: add vblank events, fix mode switching Daniil Gnusarev 2024-10-14 14:02 ` [d-kernel] [PATCH 38/39] drm: baikal-vdu: disable backlight driver loading Daniil Gnusarev 2024-10-14 14:02 ` [d-kernel] [PATCH 39/39] config-aarch64: enable more configs for baikal-m support Daniil Gnusarev 2024-10-14 14:28 ` [d-kernel] [PATCH 00/39] Support Baikal-M in un-def in p11 Vitaly Chikunov
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