[RFC] i2c: rk3x: handle dynamic clock rate changes correctly

Message ID	2185953.Zqs1uTCBnV@typ (mailing list archive)
State	New, archived
Headers	show Return-Path: <linux-rockchip-bounces+patchwork-linux-rockchip=patchwork.kernel.org@lists.infradead.org> From: Max Schwarz <max.schwarz@online.de> To: linux-rockchip@lists.infradead.org Subject: [PATCH RFC] i2c: rk3x: handle dynamic clock rate changes correctly Date: Tue, 09 Sep 2014 00:56:50 +0200 Message-ID: <2185953.Zqs1uTCBnV@typ> User-Agent: KMail/4.13.3 (Linux/3.15.7-031507-generic; KDE/4.13.3; x86_64; ; ) MIME-Version: 1.0 Cc: Huang Tao <huangtao@rock-chips.com>, Doug Anderson <dianders@chromium.org>, Addy Ke <addy.ke@rockchip.com>, Heiko =?ISO-8859-1?Q?St=FCbner?= <heiko@sntech.de>, Wolfram Sang <wsa@the-dreams.de> Precedence: list Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "Linux-rockchip" <linux-rockchip-bounces@lists.infradead.org> Errors-To: linux-rockchip-bounces+patchwork-linux-rockchip=patchwork.kernel.org@lists.infradead.org

diff --git a/drivers/i2c/busses/i2c-rk3x.c b/drivers/i2c/busses/i2c-rk3x.c index 93cfc83..825632a 100644 --- a/drivers/i2c/busses/i2c-rk3x.c +++ b/drivers/i2c/busses/i2c-rk3x.c @@ -97,6 +97,8 @@ struct rk3x_i2c { /* Hardware resources */ void __iomem *regs; struct clk *clk; + struct notifier_block clk_rate_nb; + unsigned long clk_freq; /* Settings */ unsigned int scl_frequency; @@ -428,21 +430,114 @@ out: return IRQ_HANDLED; } -static void rk3x_i2c_set_scl_rate(struct rk3x_i2c *i2c, unsigned long scl_rate) +/** + * Calculate divider value for desired SCL frequency + * + * @clk_rate: I2C input clock rate + * @scl_rate: Desired SCL rate + * @div: Divider output + * + * Return: 0 on success, -EINVAL on unreachable SCL rate. In that case + * a best-effort divider value is returned in div. + **/ +static int rk3x_i2c_calc_div(unsigned long clk_rate, unsigned long scl_rate, + unsigned int *div) { - unsigned long i2c_rate = clk_get_rate(i2c->clk); - unsigned int div; + /* Range checks */ + if (scl_rate > clk_rate / 16) { + /* Return a best effort divider */ + *div = 0; + return -EINVAL; + } + + if (scl_rate < clk_rate / (16 * 65536)) { + /* Return a best effort divider */ + *div = 0xFFFF; + return -EINVAL; + } /* set DIV = DIVH = DIVL * SCL rate = (clk rate) / (8 * (DIVH + 1 + DIVL + 1)) * = (clk rate) / (16 * (DIV + 1)) */ - div = DIV_ROUND_UP(i2c_rate, scl_rate * 16) - 1; + *div = DIV_ROUND_UP(clk_rate, scl_rate * 16) - 1; + + return 0; +} + +static void rk3x_i2c_set_scl_rate(struct rk3x_i2c *i2c, unsigned long scl_rate) +{ + unsigned long i2c_rate = clk_get_rate(i2c->clk); + unsigned int div; + + if (rk3x_i2c_calc_div(i2c_rate, scl_rate, &div) != 0) { + dev_warn(i2c->dev, "Could not reach desired SCL freq %lu Hz\n", + scl_rate + ); + } i2c_writel(i2c, (div << 16) | (div & 0xffff), REG_CLKDIV); } /** + * rk3x_i2c_clk_notifier_cb - Clock rate change callback + * @nb: Pointer to notifier block + * @event: Notification reason + * @data: Pointer to notification data object + * + * The callback checks whether a valid bus frequency can be generated after the + * change. If so, the change is acknowledged, otherwise the change is aborted. + * New dividers are written to the HW in the pre- or post change notification + * depending on the scaling direction. + * + * Code adapted from i2c-cadence.c. + * + * Return: NOTIFY_STOP if the rate change should be aborted, NOTIFY_OK + * to acknowedge the change, NOTIFY_DONE if the notification is + * considered irrelevant. + */ +static int rk3x_i2c_clk_notifier_cb(struct notifier_block *nb, unsigned long + event, void *data) +{ + struct clk_notifier_data *ndata = data; + struct rk3x_i2c *i2c = container_of(nb, struct rk3x_i2c, clk_rate_nb); + + switch (event) { + case PRE_RATE_CHANGE: + { + unsigned int div; + + if (rk3x_i2c_calc_div(ndata->new_rate, i2c->scl_frequency, + &div) != 0) { + return NOTIFY_STOP; + } + + i2c->clk_freq = ndata->new_rate; + + /* scale up */ + if (ndata->new_rate > ndata->old_rate) + rk3x_i2c_set_scl_rate(i2c, ndata->new_rate); + + return NOTIFY_OK; + } + case POST_RATE_CHANGE: + i2c->clk_freq = ndata->new_rate; + + /* scale down */ + if (ndata->new_rate < ndata->old_rate) + rk3x_i2c_set_scl_rate(i2c, ndata->new_rate); + return NOTIFY_OK; + case ABORT_RATE_CHANGE: + /* scale up */ + if (ndata->new_rate > ndata->old_rate) + rk3x_i2c_set_scl_rate(i2c, ndata->old_rate); + return NOTIFY_OK; + default: + return NOTIFY_DONE; + } +} + +/** * Setup I2C registers for an I2C operation specified by msgs, num. * * Must be called with i2c->lock held. @@ -536,9 +631,6 @@ static int rk3x_i2c_xfer(struct i2c_adapter *adap, clk_enable(i2c->clk); - /* The clock rate might have changed, so setup the divider again */ - rk3x_i2c_set_scl_rate(i2c, i2c->scl_frequency); - i2c->is_last_msg = false; /* @@ -724,16 +816,28 @@ static int rk3x_i2c_probe(struct platform_device *pdev) return ret; } + i2c->clk_rate_nb.notifier_call = rk3x_i2c_clk_notifier_cb; + ret = clk_notifier_register(i2c->clk, &i2c->clk_rate_nb); + if (ret != 0) { + dev_err(&pdev->dev, "Unable to register clock notifier\n"); + goto err_clk; + } + + i2c->clk_freq = clk_get_rate(i2c->clk); + rk3x_i2c_set_scl_rate(i2c, i2c->scl_frequency); + ret = i2c_add_adapter(&i2c->adap); if (ret < 0) { dev_err(&pdev->dev, "Could not register adapter\n"); - goto err_clk; + goto err_clk_notifier; } dev_info(&pdev->dev, "Initialized RK3xxx I2C bus at %p\n", i2c->regs); return 0; +err_clk_notifier: + clk_notifier_unregister(i2c->clk, &i2c->clk_rate_nb); err_clk: clk_unprepare(i2c->clk); return ret;

[RFC] i2c: rk3x: handle dynamic clock rate changes correctly

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