From patchwork Tue Oct 8 08:14:44 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Billy Tsai X-Patchwork-Id: 833691 Received: from TWMBX01.aspeed.com (mail.aspeedtech.com [211.20.114.72]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A159F1F8938; Tue, 8 Oct 2024 08:15:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=211.20.114.72 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728375305; cv=none; b=q+oWrumUPSYi2AedfSFv5vuYLQHEFRHOxSVDPBOGvn4ww/5JGgaLviNqXYRprc09UGGquCZYr+9RnYVb7fBkQKgqctzWxtKqRQzI8hdF/5wCd2kHU1758lmY774InzgmXYBE7p29wx1flTMVI7hVW9mRMzWgBoqDhVBomjUx/3I= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728375305; c=relaxed/simple; bh=6Dr/X4w9qdVFF3gLGFajc59wpqOKOzQWhgmVCb9iV8w=; h=From:To:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=cXxbJt2AZ6UxlmtgZXd6pwE8TzAq59PCtaxoTLQZAzCkxOrGxy/eHj022wvcly/qx0J+IW78uWNU2wb5ruSxKSJ6xcClQ28rWBVV6yYpWqHE40rrHYUqivHDU978t+1sAAHDS8jIniR5r+VCEl0WwKoZwtCWEMCoqgWupV7iouI= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=aspeedtech.com; spf=pass smtp.mailfrom=aspeedtech.com; arc=none smtp.client-ip=211.20.114.72 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=aspeedtech.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=aspeedtech.com Received: from TWMBX01.aspeed.com (192.168.0.62) by TWMBX01.aspeed.com (192.168.0.62) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1258.12; Tue, 8 Oct 2024 16:14:51 +0800 Received: from mail.aspeedtech.com (192.168.10.10) by TWMBX01.aspeed.com (192.168.0.62) with Microsoft SMTP Server id 15.2.1258.12 via Frontend Transport; Tue, 8 Oct 2024 16:14:51 +0800 From: Billy Tsai To: , , , , , , , , , , , , , , Subject: [PATCH v7 1/7] gpio: aspeed: Add the flush write to ensure the write complete. Date: Tue, 8 Oct 2024 16:14:44 +0800 Message-ID: <20241008081450.1490955-2-billy_tsai@aspeedtech.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20241008081450.1490955-1-billy_tsai@aspeedtech.com> References: <20241008081450.1490955-1-billy_tsai@aspeedtech.com> Precedence: bulk X-Mailing-List: linux-gpio@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Performing a dummy read ensures that the register write operation is fully completed, mitigating any potential bus delays that could otherwise impact the frequency of bitbang usage. E.g., if the JTAG application uses GPIO to control the JTAG pins (TCK, TMS, TDI, TDO, and TRST), and the application sets the TCK clock to 1 MHz, the GPIO's high/low transitions will rely on a delay function to ensure the clock frequency does not exceed 1 MHz. However, this can lead to rapid toggling of the GPIO because the write operation is POSTed and does not wait for a bus acknowledgment. Fixes: 361b79119a4b ("gpio: Add Aspeed driver") Reviewed-by: Andrew Jeffery Signed-off-by: Billy Tsai --- drivers/gpio/gpio-aspeed.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/gpio/gpio-aspeed.c b/drivers/gpio/gpio-aspeed.c index 04c03402db6d..98551b7f6de2 100644 --- a/drivers/gpio/gpio-aspeed.c +++ b/drivers/gpio/gpio-aspeed.c @@ -406,6 +406,8 @@ static void __aspeed_gpio_set(struct gpio_chip *gc, unsigned int offset, gpio->dcache[GPIO_BANK(offset)] = reg; iowrite32(reg, addr); + /* Flush write */ + ioread32(addr); } static void aspeed_gpio_set(struct gpio_chip *gc, unsigned int offset,