From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [213.167.242.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C3978139566; Thu, 16 Jan 2025 10:05:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.167.242.64 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737021938; cv=none; b=gUosuLJnv33eYwcIjlNULr0kua+QGsnbPay7glcSYLEP+Bhnk2/aPjLDLxXZHWHcsmskdehzPWDCrCSZykITQJYdqY4JIT85xCCjk6oH9qTvTmz3ZepOruonc3gy2xZHcLzS0I/KtvMo6XLdSKA2W71HVjrPIFZ7KZgCX9PmKkQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737021938; c=relaxed/simple; bh=z8wJtdOhffsKfj1mM3OHQ70mutizLA2iDQi4p9K/OJk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=OAyXPJSeMuzijWg9xngQIUgfvLnga0IM1POMtfxMSmcdaFgAyxrYWEBC+gMQZ+KJSVKm7//8Q7tyT2VWcmBd4PSvEwvrjhNWwnVjYBSkQ/TWg0haOWPJUbMZhNJgI0IhCfUjEyhKThOroJS5khmkF1KmqqQoBR4XtrbCJOXxJBU= ARC-Authentication-Results:i=1; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hi, On 16/01/2025 11:58, Sakari Ailus wrote: > Moi, > > On Wed, Jan 15, 2025 at 06:04:40PM +0200, Tomi Valkeinen wrote: >> On 15/01/2025 16:26, Sakari Ailus wrote: >>> Moi, >>> >>> On Fri, Jan 10, 2025 at 11:14:16AM +0200, Tomi Valkeinen wrote: >>>> From: Jai Luthra >>>> >>>> UB9702 supports spread-spectrum clock generation for the back-channel >>>> clock, which is futher used by serializers in synchronous mode to >>>> generate the forward-channel clock, which can help reduce peak EMI >>>> energy. The SSCG is common to all RX ports, so it can only be used if >>>> all the ports are in the same mode. >>>> >>>> Add basic support for SSCG by adding a module parameter to enable the >>>> SSCG. The SSCG uses hardcoded configurationg, with 0.5% center-spread at >>>> 33kHz modulation rate. See datasheet if different configuration is >>>> required. >>>> >>>> Signed-off-by: Jai Luthra >>>> Signed-off-by: Tomi Valkeinen >>>> --- >>>> drivers/media/i2c/ds90ub960.c | 102 ++++++++++++++++++++++++++++++++++++++++++ >>>> 1 file changed, 102 insertions(+) >>>> >>>> diff --git a/drivers/media/i2c/ds90ub960.c b/drivers/media/i2c/ds90ub960.c >>>> index f6d6c2fe12cd..a534d077f045 100644 >>>> --- a/drivers/media/i2c/ds90ub960.c >>>> +++ b/drivers/media/i2c/ds90ub960.c >>>> @@ -52,6 +52,10 @@ >>>> #include >>>> #include >>>> +static bool ub960_enable_sscg; >>>> +module_param_named(enable_sscg, ub960_enable_sscg, bool, 0644); >>>> +MODULE_PARM_DESC(enable_sscg, "Enable SSCG (if available)"); >>> >>> Shouldn't this come from DT instead? >> >> SSCG is an option to use or not to use, based on what the user wants. DT >> should describe the hardware. >> >> A module parameter is bad for this, though, as it's then used for all ub960 >> devices... But I'm not sure what other options we have. We need to have it >> at probe time. >> >> Probably the whole driver could be changed to not connect the serializers at >> probe, but instead would offer a set of userspace APIs to enable/disable >> SSCG, and to enable the links. But that brings in its own set of problems, >> as the links are used for i2c communication to the ser and sensor, not to >> mention new userspace APIs which always complicates things. > > Typically determining whether you need spread spectrum signalling is highly > specific to the board. I wonder if this topic has been discussed (and > possibly somehow resolved) for other subsystems. CSI-2 appears to allow for > spread spectrum clocks but I don't think I've seen that implemeted > anywhere, scrambling may be more popular (but also that is right now > unsupported but could be supported, probably this would be best to consider > in conjunction with other CSI-2 parameters). Well, I personally would rather have this option in the DT, so I'm all for it =). We can change this to a DT parameter, and see how the DT maintainers react. Tomi