Re: [PATCH v4 1/4] dt-bindings: media: imx258: add bindings for IMX258 sensor
From: Krzysztof Kozlowski <krzk@kernel.org>
Date: 2020-09-29 09:46:43
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On Tue, Sep 29, 2020 at 12:40:46PM +0300, Sakari Ailus wrote:
On Tue, Sep 29, 2020 at 11:18:46AM +0200, Krzysztof Kozlowski wrote:quoted
On Tue, 29 Sep 2020 at 11:15, Sakari Ailus [off-list ref] wrote:quoted
Hi Krzysztof, On Wed, Sep 23, 2020 at 05:21:26PM +0200, Krzysztof Kozlowski wrote:quoted
Add bindings for the IMX258 camera sensor. The bindings, just like the driver, are quite limited, e.g. do not support regulator supplies. Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org> --- Changes since v3: 1. Document also two lane setup. Changes since v2: 1. Remove clock-frequency, add reset GPIOs, add supplies.Oops. I missed this one. How does the driver know the appropriate clock frequency for the platform if it's not in DT? The sensor supports a range of frequencies, not a single frequency. Could you add clock-frequency back?Not really, it was removed on Rob's request. The bindings do not describe driver's behavior so how the driver gets frequency should not be part of the bindings. Also it's not a real problem - the driver just calls clk_get_rate().How is the rate determined? I mean, many ISPs or CSI-2 receivers that provide the clock are also capable of using a variety of frequencies. But only one can be used on the platform in general.
Having "clock-frequency" property in DTS did not solve that. It has no effect on actual frequency.
Where does it come from if it's not in DT?
The frequency is either chosen by consumer (imx258) or pre-assigned from DT, but not with "clock-frequency" property. There are generic properties for this: assigned-clocks, assigned-clock-rates and assigned-clock-parents. These properties should be added to DTS if additionalProperties is false, which is the case here... so I could add them. My DTS anyway does not use them, as the clock is generated internally on a camera board so I don't have a control over it. Best regards, Krzysztof
Using another frequency generally leads to failure later on as the desired link frequency likely is not available for a random external clock frequency.
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