GPIO Acquire/Release Semantics for 'AI Camera' #6884
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6by9
reviewed
Jun 5, 2025
Add support for the 'gpio-gate-clock-releasing' compatible string. The behaviour is identical to that of 'gpio-gate-clock' but the gpio is acquired on 'enable' and released on 'disable'. Signed-off-by: Richard Oliver <richard.oliver@raspberrypi.com>
Document the gpio-gate-clock-releasing compatible string that enables acquire/release GPIO semantics on gpio-gated clocks. Signed-off-by: Richard Oliver <richard.oliver@raspberrypi.com>
The clock using by IMX500 in 'AI Camera' is gpio-gated. The GPIO used is provided by an I2C-controlled rpi-rp2040-gpio-bridge on 'AI Camera'. Both the IMX500 and gpio-bridge share a common regulator for their power supply. Using 'gpio-gate-clock', the 'AI Camera' will never be powered-down as the GPIO provided by the gpio-bridge is always claimed by the clock driver. Switching to 'gpio-gate-clock-releasing' causes the GPIO to be released by the clock driver when the clock is not needed. This allows 'AI Camera' to be powered-down. Signed-off-by: Richard Oliver <richard.oliver@raspberrypi.com>
This change amends various error-paths in imx500_start_streaming() to ensure that pm_runtime refcounts do not remain erroneously incremented on failure. Signed-off-by: Richard Oliver <richard.oliver@raspberrypi.com>
When the imx500 driver is used as part of the 'AI Camera', the poweroff state is never reached as the camera and gpio driver share a regulator. By releasing the GPIOs when they are not in use, 'AI Camera' is able to achieve a powered-down state. Signed-off-by: Richard Oliver <richard.oliver@raspberrypi.com>
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I believe all the review comments have been addressed. Are we happy for this to go in @6by9? |
6by9
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Jun 9, 2025
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Looks good to me. |
pelwell
reviewed
Jun 9, 2025
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Given that there is no reference counting and no intention of re-entrancy or simultaneous use (at least by this driver), doesn't it point to a programming error for clk_gpio_gate_is_acquired to find that the GPIO is already acquired? In which case, given that clk_gpio_gate_acquire has an error return, why not drop clk_gpio_gate_is_acquired altogether and call ...acquire unconditionally?
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| struct clk_gpio *clk = to_clk_gpio(hw); | ||
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| return clk->gpiod; |
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Here you are declaring non-zero to indicate success (although I'd have preferred !!clk->gpiod to make the type conversion more obvious), but clk_gpio_get_acquire leaves it containing an error code on failure.
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