linux-kernel - Re: [PATCH v3 10/13] media: v4l2-fwnode: Update V4L2_FWNODE_CSI2_MAX_DATA

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Message-ID: <23de1994-0a3e-179b-2c2f-b41917d02585@nvidia.com>
Date:   Tue, 8 Dec 2020 12:27:22 -0800
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Sakari Ailus <sakari.ailus@....fi>,
        Hans Verkuil <hverkuil@...all.nl>
CC:     <thierry.reding@...il.com>, <jonathanh@...dia.com>,
        <robh+dt@...nel.org>, <bparrot@...com>, <mchehab@...nel.org>,
        <linux-media@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Subject: Re: [PATCH v3 10/13] media: v4l2-fwnode: Update
 V4L2_FWNODE_CSI2_MAX_DATA_LANES to 8


On 12/8/20 11:59 AM, Sakari Ailus wrote:
> Hi Hans,
>
> On Mon, Dec 07, 2020 at 11:47:38AM +0100, Hans Verkuil wrote:
>> On 03/12/2020 19:59, Sowjanya Komatineni wrote:
>>> Some CSI2 receivers support 8 data lanes.
>>>
>>> So, this patch updates CSI2 maximum data lanes to be 8.
>>>
>>> Signed-off-by: Sowjanya Komatineni <skomatineni@...dia.com>
>>> ---
>>>   drivers/media/platform/ti-vpe/cal-camerarx.c | 2 +-
>>>   include/media/v4l2-fwnode.h                  | 2 +-
>>>   2 files changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/media/platform/ti-vpe/cal-camerarx.c b/drivers/media/platform/ti-vpe/cal-camerarx.c
>>> index 806cbf1..47e2143 100644
>>> --- a/drivers/media/platform/ti-vpe/cal-camerarx.c
>>> +++ b/drivers/media/platform/ti-vpe/cal-camerarx.c
>>> @@ -534,7 +534,7 @@ static int cal_camerarx_parse_dt(struct cal_camerarx *phy)
>>>   {
>>>   	struct v4l2_fwnode_endpoint *endpoint = &phy->endpoint;
>>>   	struct device_node *ep_node;
>>> -	char data_lanes[V4L2_FWNODE_CSI2_MAX_DATA_LANES * 2];
>>> +	char data_lanes[V4L2_FWNODE_CSI2_MAX_DATA_LANES];
>>>   	unsigned int i;
>>>   	int ret;
>>>   
>> I'm not so sure about this change: it relies on the implicit knowledge that
>> this cal driver can handle only 4 lanes max, so that doubling
>> V4L2_FWNODE_CSI2_MAX_DATA_LANES is the same as the old 'V4L2_FWNODE_CSI2_MAX_DATA_LANES * 2'.
>>
>> I think we should either keep the existing code (which means data_lanes
>> is now larger than needed, so stack usage increases by 8 bytes), or perhaps
>> create a new define for this driver like CAL_MAX_DATA_LANES and use that.
>>
>> In my opinion the original code should just be kept, but I've CC-ed Laurent
>> on this to hear what he thinks.
> I further looked at the code there and it does *depend* on a particular
> value of V4L2_FWNODE_CSI2_MAX_DATA_LANES. That needs to be fixed. This part
> can (or should) be dropped from the patch though.
>
Thanks Sakari and Hans.

OK. Will drop updating cal-camerarx.c from this patch in next version.