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bh=5qg09P4fJgr+a4V0kkb6T7N6RFRG+NYeOfMhOPT4/Dc=; b=TparB7bKkzIKotxKx48zZ5jSnJb+iHPW5aNC3ISSCyDD3+9cx5ejfAbS/04IV6h9gb msSOu9rlthGEUFyHI4FMpJ9yHSRYIH6IUspUYmWrT2LqcFmO66f02mLsh3TQxQ9TsXC8 yQZUJP1EpE0cdxixM1flk7zhF79N5sWIqZN41HMVcFoaVE47nOHPRZP/466HhO5M3z96 9oyakjrPbC0JFWuOsLZPSaLHD3Nq/i3xvAO6wH5VosWVGMxnJJeGoBcXVBfaH2AZsEZF PMan3DHyOngU9Fg4HPIUucd9X/YCtp+P+hvbxiiHLpcEOyHvF5jgxykRX5AMKcD60UJV Fwew== X-Gm-Message-State: AGi0PubOo3oMpJ226bbM923fg+3MjKV0BMEL89YGt/pWcAPSr3GrH/Ym Uzz6aK/Iut4uyrC5mcMB0KbqDA== X-Google-Smtp-Source: APiQypKnhe6XWsZGMGHpEQeihQ6bHdJTrY0q2pMJXMds500wkrvQkChdn9JC76eSbx48i4opUzXQoA== X-Received: by 2002:a17:90a:d985:: with SMTP id d5mr5793380pjv.171.1588088891211; Tue, 28 Apr 2020 08:48:11 -0700 (PDT) Received: from localhost ([2620:15c:202:1:4fff:7a6b:a335:8fde]) by smtp.gmail.com with ESMTPSA id v1sm2392709pjs.36.2020.04.28.08.48.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 28 Apr 2020 08:48:10 -0700 (PDT) Date: Tue, 28 Apr 2020 08:48:09 -0700 From: Matthias Kaehlcke To: Akash Asthana Cc: gregkh@linuxfoundation.org, agross@kernel.org, bjorn.andersson@linaro.org, wsa@the-dreams.de, broonie@kernel.org, mark.rutland@arm.com, robh+dt@kernel.org, georgi.djakov@linaro.org, linux-i2c@vger.kernel.org, linux-spi@vger.kernel.org, devicetree@vger.kernel.org, swboyd@chromium.org, mgautam@codeaurora.org, linux-arm-msm@vger.kernel.org, linux-serial@vger.kernel.org, dianders@chromium.org, evgreen@chromium.org Subject: Re: [PATCH V4 4/9] soc: qcom-geni-se: Add interconnect support to fix earlycon crash Message-ID: <20200428154809.GH4525@google.com> References: <1586946198-13912-1-git-send-email-akashast@codeaurora.org> <1586946198-13912-5-git-send-email-akashast@codeaurora.org> <20200416003112.GA199755@google.com> <146cf8db-3c09-39a6-2886-bec0db289948@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <146cf8db-3c09-39a6-2886-bec0db289948@codeaurora.org> Sender: linux-serial-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org Hi Akash, On Tue, Apr 28, 2020 at 03:51:44PM +0530, Akash Asthana wrote: > Hi Matthias, > > On 4/16/2020 6:01 AM, Matthias Kaehlcke wrote: > > Hi Akash, > > > > On Wed, Apr 15, 2020 at 03:53:13PM +0530, Akash Asthana wrote: ... > > > diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c > > > index 6119090..8c5d97c 100644 > > > --- a/drivers/tty/serial/qcom_geni_serial.c > > > +++ b/drivers/tty/serial/qcom_geni_serial.c > > > @@ -1090,6 +1090,12 @@ static void qcom_geni_serial_earlycon_write(struct console *con, > > > __qcom_geni_serial_console_write(&dev->port, s, n); > > > } > > > +static int qcom_geni_serial_earlycon_exit(struct console *con) > > > +{ > > > + geni_remove_earlycon_icc_vote(); > > > + return 0; > > > +} > > > + > > > static int __init qcom_geni_serial_earlycon_setup(struct earlycon_device *dev, > > > const char *opt) > > > { > > > @@ -1135,6 +1141,7 @@ static int __init qcom_geni_serial_earlycon_setup(struct earlycon_device *dev, > > > writel(stop_bit_len, uport->membase + SE_UART_TX_STOP_BIT_LEN); > > > dev->con->write = qcom_geni_serial_earlycon_write; > > > + dev->con->exit = qcom_geni_serial_earlycon_exit; > > The idea of using the exit handler of the early console to remove the > > votes seemed appealing at first, however it has a drawback: the bandwidth > > requests in geni_se_probe() are always made when CONFIG_SERIAL_EARLYCON=y, > > also when the system doesn't actually use an early console. On such a > > system the votes would never be removed. > > > > A possible alternative could seem to remove the vote at the end of > > qcom_geni_serial_probe() of the 'normal' console, but it has a similar > > problem: the system could not even have a normal console. One could > > possibly argue that CONFIG_SERIAL_QCOM_GENI_CONSOLE shouldn't be set > > on such a system, however it could be enabled to have a console for > > development, and in production the same kernel config is used, but > > with the console disabled through the device tree. > > > > I don't really have a good idea at this point, maybe we just need > > something as ugly as a delayed work to remove the votes. Other > > suggestions are welcome :) > > I think we can do something like below. Before voting we are checking > whether earlyconsole ("qcom_geni") exits or not.  The name is fixed from > earlycon declaration file@drivers/tty/serial/qcom_geni_serial.c > > OF_EARLYCON_DECLARE(qcom_geni, "qcom,geni-debug-uart", >                                 qcom_geni_serial_earlycon_setup); > > ==================================================================================== > > @@ -809,6 +809,8 @@ static int geni_se_probe(struct platform_device *pdev) >         struct device *dev = &pdev->dev; >         struct resource *res; >         struct geni_wrapper *wrapper; > +       struct console *bcon = NULL; nit: initialization is not needed > +       int earlycon_present = 0; >         int ret; > >         wrapper = devm_kzalloc(dev, sizeof(*wrapper), GFP_KERNEL); > @@ -832,6 +834,15 @@ static int geni_se_probe(struct platform_device *pdev) >         } > >  #ifdef CONFIG_SERIAL_EARLYCON > +       if (console_drivers) > +               for_each_console(bcon) > +                       if (!strcmp(bcon->name, "qcom_geni")) { > +                               earlycon_present = 1; > +                               break; > +                       } > +       if(!earlycon_present) > +               goto exit; > + >         wrapper->to_core.path = devm_of_icc_get(dev, "qup-core"); >         if (IS_ERR(wrapper->to_core.path)) >                 return PTR_ERR(wrapper->to_core.path); > @@ -858,6 +869,7 @@ static int geni_se_probe(struct platform_device *pdev) >         of_node_put(pdev->dev.of_node); >  #endif > > +exit: >         dev_set_drvdata(dev, wrapper); >         dev_dbg(dev, "GENI SE Driver probed\n"); >         return devm_of_platform_populate(dev); > This should work as long as the early console is always set up before geni_se is probed, which seems a safe assumption.