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Thu, 24 Sep 2026 00:21:54 -0700 (PDT) Received: from AHERLNXVDANI01.lgs-net.com ([193.8.40.126]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49fe5bb9891sm41051975e9.6.2026.09.24.00.21.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 24 Sep 2026 00:21:54 -0700 (PDT) From: =?UTF-8?q?Daniel=20Via=C3=B1o?= To: Alexandre Belloni Cc: Michal Simek , linux-rtc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, =?UTF-8?q?Daniel=20Via=C3=B1o?= , stable@vger.kernel.org Subject: [PATCH] rtc: zynqmp: Enable crystal oscillator in initialization Date: Thu, 24 Sep 2026 09:19:16 +0200 Message-ID: <20260924071917.80004-1-danividanivi@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-rtc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Enable the RTC crystal oscillator bit in the control register (RTC_CTRL, offset 0x40) during driver initialization. Although the RTC_OSC_EN macro was defined when the driver was originally introduced, it was never asserted in xlnx_init_rtc(). On cold boots, after battery exhaustion, or on platforms where firmware does not pre-initialize RTC_CTRL, the oscillator remains disabled and the counter never ticks. Asserting RTC_OSC_EN alongside RTC_BATT_EN ensures the oscillator starts without relying on bootloader initialization. Per the Zynq UltraScale+ TRM (UG1085), bit 24 (OSC_CNTRL) is a static level enable for the crystal inverter rather than an edge-triggered reset; re-asserting it when the oscillator is already running is a non-destructive no-op that does not glitch or reset the ticking counters. Tested on Zynq UltraScale+ hardware, confirming that the counter freezes when RTC_OSC_EN is cleared, advances reliably once enabled, and is unaffected when re-asserted while running. Fixes: 11143c19eb57 ("rtc: add xilinx zynqmp rtc driver") Cc: stable@vger.kernel.org Signed-off-by: Daniel Viaño --- drivers/rtc/rtc-zynqmp.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/drivers/rtc/rtc-zynqmp.c b/drivers/rtc/rtc-zynqmp.c index 5bcb7536e973..278705ec09f5 100644 --- a/drivers/rtc/rtc-zynqmp.c +++ b/drivers/rtc/rtc-zynqmp.c @@ -167,9 +167,12 @@ static void xlnx_init_rtc(struct xlnx_rtc_dev *xrtcdev) { u32 rtc_ctrl; - /* Enable RTC switch to battery when VCC_PSAUX is not available */ + /* + * Enable crystal oscillator, and enable RTC switch to battery + * when VCC_PSAUX is not available. + */ rtc_ctrl = readl(xrtcdev->reg_base + RTC_CTRL); - rtc_ctrl |= RTC_BATT_EN; + rtc_ctrl |= RTC_BATT_EN | RTC_OSC_EN; writel(rtc_ctrl, xrtcdev->reg_base + RTC_CTRL); } -- 2.53.0