| Message ID | 20220411132107.136369-1-angelogioacchino.delregno@collabora.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] i2c: mediatek: Optimize master_xfer() and avoid circular locking | expand |
Il 11/04/22 15:21, AngeloGioacchino Del Regno ha scritto: > Especially (but not only) during probe, it may happen that multiple > devices are communicating via i2c (or multiple i2c busses) and > sometimes while others are probing asynchronously. > For example, a Cr50 TPM may be filling entropy (or userspace may be > reading random data) while the rt5682 (i2c) codec driver reads/sets > some registers, like while getting/setting a clock's rate, which > happens both during probe and during system operation. > > In this driver, the mtk_i2c_transfer() function (which is the i2c > .master_xfer() callback) was granularly managing the clocks by > performing a clk_bulk_prepare_enable() to start them and its inverse. > This is not only creating possible circular locking dependencies in > the some cases (like former explanation), but it's also suboptimal, > as clk_core prepare/unprepare operations are using mutex locking, > which creates a bit of unwanted overhead (for example, i2c trackpads > will call master_xfer() every few milliseconds!). > > With this commit, we avoid both the circular locking and additional > overhead by changing how we handle the clocks in this driver: > - Prepare the clocks during probe (and PM resume) > - Enable/disable clocks in mtk_i2c_transfer() > - Unprepare the clocks only for driver removal (and PM suspend) > > For the sake of providing a full explanation: during probe, the > clocks are not only prepared but also enabled, as this is needed > for some hardware initialization but, after that, we are disabling > but not unpreparing them, leaving an expected state for the > aforementioned clock handling strategy. > > Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com> > Tested-by: Nícolas F. R. A. Prado <nfraprado@collabora.com> Hello, this is a friendly ping to not let this be forgotten. Cheers, Angelo > --- > > v2: Fixed typos in commit description > > drivers/i2c/busses/i2c-mt65xx.c | 11 +++++++---- > 1 file changed, 7 insertions(+), 4 deletions(-) >
On Mon, 2022-04-11 at 15:21 +0200, AngeloGioacchino Del Regno wrote: > Especially (but not only) during probe, it may happen that multiple > devices are communicating via i2c (or multiple i2c busses) and > sometimes while others are probing asynchronously. > For example, a Cr50 TPM may be filling entropy (or userspace may be > reading random data) while the rt5682 (i2c) codec driver reads/sets > some registers, like while getting/setting a clock's rate, which > happens both during probe and during system operation. > > In this driver, the mtk_i2c_transfer() function (which is the i2c > .master_xfer() callback) was granularly managing the clocks by > performing a clk_bulk_prepare_enable() to start them and its inverse. > This is not only creating possible circular locking dependencies in > the some cases (like former explanation), but it's also suboptimal, > as clk_core prepare/unprepare operations are using mutex locking, > which creates a bit of unwanted overhead (for example, i2c trackpads > will call master_xfer() every few milliseconds!). > > With this commit, we avoid both the circular locking and additional > overhead by changing how we handle the clocks in this driver: > - Prepare the clocks during probe (and PM resume) > - Enable/disable clocks in mtk_i2c_transfer() > - Unprepare the clocks only for driver removal (and PM suspend) > > For the sake of providing a full explanation: during probe, the > clocks are not only prepared but also enabled, as this is needed > for some hardware initialization but, after that, we are disabling > but not unpreparing them, leaving an expected state for the > aforementioned clock handling strategy. > > Signed-off-by: AngeloGioacchino Del Regno < > angelogioacchino.delregno@collabora.com> > Tested-by: Nícolas F. R. A. Prado <nfraprado@collabora.com> Reviewed-by: Qii Wang <qii.wang@mediatek.com> > --- > > v2: Fixed typos in commit description > > drivers/i2c/busses/i2c-mt65xx.c | 11 +++++++---- > 1 file changed, 7 insertions(+), 4 deletions(-) > >
On Mon, Apr 11, 2022 at 03:21:07PM +0200, AngeloGioacchino Del Regno wrote: > Especially (but not only) during probe, it may happen that multiple > devices are communicating via i2c (or multiple i2c busses) and > sometimes while others are probing asynchronously. > For example, a Cr50 TPM may be filling entropy (or userspace may be > reading random data) while the rt5682 (i2c) codec driver reads/sets > some registers, like while getting/setting a clock's rate, which > happens both during probe and during system operation. > > In this driver, the mtk_i2c_transfer() function (which is the i2c > .master_xfer() callback) was granularly managing the clocks by > performing a clk_bulk_prepare_enable() to start them and its inverse. > This is not only creating possible circular locking dependencies in > the some cases (like former explanation), but it's also suboptimal, > as clk_core prepare/unprepare operations are using mutex locking, > which creates a bit of unwanted overhead (for example, i2c trackpads > will call master_xfer() every few milliseconds!). > > With this commit, we avoid both the circular locking and additional > overhead by changing how we handle the clocks in this driver: > - Prepare the clocks during probe (and PM resume) > - Enable/disable clocks in mtk_i2c_transfer() > - Unprepare the clocks only for driver removal (and PM suspend) > > For the sake of providing a full explanation: during probe, the > clocks are not only prepared but also enabled, as this is needed > for some hardware initialization but, after that, we are disabling > but not unpreparing them, leaving an expected state for the > aforementioned clock handling strategy. > > Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com> > Tested-by: Nícolas F. R. A. Prado <nfraprado@collabora.com> Applied to for-next, thanks!
diff --git a/drivers/i2c/busses/i2c-mt65xx.c b/drivers/i2c/busses/i2c-mt65xx.c index f651d3e124d6..bdecb78bfc26 100644 --- a/drivers/i2c/busses/i2c-mt65xx.c +++ b/drivers/i2c/busses/i2c-mt65xx.c @@ -1177,7 +1177,7 @@ static int mtk_i2c_transfer(struct i2c_adapter *adap, int left_num = num; struct mtk_i2c *i2c = i2c_get_adapdata(adap); - ret = clk_bulk_prepare_enable(I2C_MT65XX_CLK_MAX, i2c->clocks); + ret = clk_bulk_enable(I2C_MT65XX_CLK_MAX, i2c->clocks); if (ret) return ret; @@ -1231,7 +1231,7 @@ static int mtk_i2c_transfer(struct i2c_adapter *adap, ret = num; err_exit: - clk_bulk_disable_unprepare(I2C_MT65XX_CLK_MAX, i2c->clocks); + clk_bulk_disable(I2C_MT65XX_CLK_MAX, i2c->clocks); return ret; } @@ -1412,7 +1412,7 @@ static int mtk_i2c_probe(struct platform_device *pdev) return ret; } mtk_i2c_init_hw(i2c); - clk_bulk_disable_unprepare(I2C_MT65XX_CLK_MAX, i2c->clocks); + clk_bulk_disable(I2C_MT65XX_CLK_MAX, i2c->clocks); ret = devm_request_irq(&pdev->dev, irq, mtk_i2c_irq, IRQF_NO_SUSPEND | IRQF_TRIGGER_NONE, @@ -1439,6 +1439,8 @@ static int mtk_i2c_remove(struct platform_device *pdev) i2c_del_adapter(&i2c->adap); + clk_bulk_unprepare(I2C_MT65XX_CLK_MAX, i2c->clocks); + return 0; } @@ -1448,6 +1450,7 @@ static int mtk_i2c_suspend_noirq(struct device *dev) struct mtk_i2c *i2c = dev_get_drvdata(dev); i2c_mark_adapter_suspended(&i2c->adap); + clk_bulk_unprepare(I2C_MT65XX_CLK_MAX, i2c->clocks); return 0; } @@ -1465,7 +1468,7 @@ static int mtk_i2c_resume_noirq(struct device *dev) mtk_i2c_init_hw(i2c); - clk_bulk_disable_unprepare(I2C_MT65XX_CLK_MAX, i2c->clocks); + clk_bulk_disable(I2C_MT65XX_CLK_MAX, i2c->clocks); i2c_mark_adapter_resumed(&i2c->adap);