From patchwork Mon Jan 24 21:38:49 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Zev Weiss X-Patchwork-Id: 536966 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id BBCC8C433EF for ; Tue, 25 Jan 2022 02:19:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2364012AbiAYCSn (ORCPT ); Mon, 24 Jan 2022 21:18:43 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58196 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2366255AbiAXXwd (ORCPT ); Mon, 24 Jan 2022 18:52:33 -0500 Received: from thorn.bewilderbeest.net (thorn.bewilderbeest.net [IPv6:2605:2700:0:5::4713:9cab]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A7700C0419DA for ; Mon, 24 Jan 2022 13:46:00 -0800 (PST) Received: from hatter.bewilderbeest.net (174-21-190-118.tukw.qwest.net [174.21.190.118]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: zev) by thorn.bewilderbeest.net (Postfix) with ESMTPSA id 3B729631; Mon, 24 Jan 2022 13:39:02 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bewilderbeest.net; s=thorn; t=1643060342; bh=TQdtq1xEutLhm8c8Qf43KWKlCveAJESF7JMSVl2lQuE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=hMfoF86skJdkCyhEGSaUgjYLxT7NFfz/RdR70RDZMTLwxal26CNO6UsQK8B6hqm3j n8yAzLtn0n7X+oQvwPYeg7mcof4TiEA5R4lrtt8us2zq+byDEqylikZHU5TCw91Vjz o8KNozgZwirHfaKJ2SK4CpaYp6fMA+Eu3aI2lcxI= From: Zev Weiss To: linux-i2c@vger.kernel.org, Guenter Roeck , Peter Rosin Cc: Zev Weiss , openbmc@lists.ozlabs.org, linux-kernel@vger.kernel.org Subject: [PATCH 1/2] i2c: mux: pca9541: add delayed-release support Date: Mon, 24 Jan 2022 13:38:49 -0800 Message-Id: <20220124213850.3766-2-zev@bewilderbeest.net> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20220124213850.3766-1-zev@bewilderbeest.net> References: <20220124213850.3766-1-zev@bewilderbeest.net> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-i2c@vger.kernel.org For heavily-utilized i2c busses, the overhead of reacquiring bus ownership on every transaction can be quite substantial. By delaying the release of the bus (in anticipation of another transaction needing to re-acquire ownership in the near future), we can reduce the overhead significantly -- a subsequent transaction that arrives within the delay window can merely verify that we still own it. The new "release-delay-us" DT property specifies a number of microseconds to wait after a transaction before releasing the bus (zero by default so as to preserve the existing behavior of releasing it immediately). Signed-off-by: Zev Weiss Reviewed-by: Joel Stanley --- drivers/i2c/muxes/i2c-mux-pca9541.c | 56 ++++++++++++++++++++++++----- 1 file changed, 47 insertions(+), 9 deletions(-) diff --git a/drivers/i2c/muxes/i2c-mux-pca9541.c b/drivers/i2c/muxes/i2c-mux-pca9541.c index 6daec8d3d331..76269bf9f9ca 100644 --- a/drivers/i2c/muxes/i2c-mux-pca9541.c +++ b/drivers/i2c/muxes/i2c-mux-pca9541.c @@ -19,6 +19,7 @@ #include #include #include +#include #include #include #include @@ -75,6 +76,8 @@ struct pca9541 { struct i2c_client *client; unsigned long select_timeout; unsigned long arb_timeout; + unsigned long release_delay; + struct delayed_work release_work; }; static const struct i2c_device_id pca9541_id[] = { @@ -127,8 +130,11 @@ static int pca9541_reg_read(struct i2c_client *client, u8 command) * Arbitration management functions */ -/* Release bus. Also reset NTESTON and BUSINIT if it was set. */ -static void pca9541_release_bus(struct i2c_client *client) +/* + * Release bus. Also reset NTESTON and BUSINIT if it was set. + * client->adapter must already be locked. + */ +static void __pca9541_release_bus(struct i2c_client *client) { int reg; @@ -138,6 +144,13 @@ static void pca9541_release_bus(struct i2c_client *client) (reg & PCA9541_CTL_NBUSON) >> 1); } +static void pca9541_release_bus(struct i2c_client *client) +{ + i2c_lock_bus(client->adapter, I2C_LOCK_SEGMENT); + __pca9541_release_bus(client); + i2c_unlock_bus(client->adapter, I2C_LOCK_SEGMENT); +} + /* * Arbitration is defined as a two-step process. A bus master can only activate * the slave bus if it owns it; otherwise it has to request ownership first. @@ -254,6 +267,9 @@ static int pca9541_select_chan(struct i2c_mux_core *muxc, u32 chan) unsigned long timeout = jiffies + ARB2_TIMEOUT; /* give up after this time */ + if (data->release_delay) + cancel_delayed_work_sync(&data->release_work); + data->arb_timeout = jiffies + ARB_TIMEOUT; /* force bus ownership after this time */ @@ -276,10 +292,21 @@ static int pca9541_release_chan(struct i2c_mux_core *muxc, u32 chan) struct pca9541 *data = i2c_mux_priv(muxc); struct i2c_client *client = data->client; - pca9541_release_bus(client); + if (data->release_delay) + schedule_delayed_work(&data->release_work, data->release_delay); + else + __pca9541_release_bus(client); + return 0; } +static void pca9541_release_workfn(struct work_struct *work) +{ + struct pca9541 *data = container_of(work, struct pca9541, release_work.work); + + pca9541_release_bus(data->client); +} + /* * I2C init/probing/exit functions */ @@ -289,18 +316,13 @@ static int pca9541_probe(struct i2c_client *client, struct i2c_adapter *adap = client->adapter; struct i2c_mux_core *muxc; struct pca9541 *data; + u32 release_delay_us; int ret; if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_BYTE_DATA)) return -ENODEV; - /* - * I2C accesses are unprotected here. - * We have to lock the I2C segment before releasing the bus. - */ - i2c_lock_bus(adap, I2C_LOCK_SEGMENT); pca9541_release_bus(client); - i2c_unlock_bus(adap, I2C_LOCK_SEGMENT); /* Create mux adapter */ @@ -313,6 +335,14 @@ static int pca9541_probe(struct i2c_client *client, data = i2c_mux_priv(muxc); data->client = client; + if (!device_property_read_u32(&client->dev, "release-delay-us", &release_delay_us)) { + data->release_delay = usecs_to_jiffies(release_delay_us); + ret = devm_delayed_work_autocancel(&client->dev, &data->release_work, + pca9541_release_workfn); + if (ret) + return ret; + } + i2c_set_clientdata(client, muxc); ret = i2c_mux_add_adapter(muxc, 0, 0, 0); @@ -328,6 +358,14 @@ static int pca9541_probe(struct i2c_client *client, static int pca9541_remove(struct i2c_client *client) { struct i2c_mux_core *muxc = i2c_get_clientdata(client); + struct pca9541 *data = i2c_mux_priv(muxc); + + /* + * Ensure the bus is released (in case the device gets destroyed + * before release_work runs). + */ + if (data->release_delay) + pca9541_release_bus(client); i2c_mux_del_adapters(muxc); return 0;