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 AA73A18784C; Thu, 24 Oct 2024 12:26:44 +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=1729772807; cv=none; b=kTsAQycdwaLv4f6Ugt9wyA7Iw4WVS8RiLMwT6td01SeFwA3xmPA+tW1jEXgTtP/o+gL88lRDzW1v1DDCaM5TjV4ZBRoIRB1xz/7N2WRMxgZ5BGl5/w15RUr4foXL7t8YnxaSgZTRiSGcJzq9sJLtLUnnjrmCrWTkZ5mQIV7Fg4w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729772807; c=relaxed/simple; bh=mKwfBFb98YUVWR1h6VvhXb0DPxsXbBhje3HQ1yKmQao=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=QpPasKsWGqtFxyacfCG8GTDOdPtXif948qqld1XajAcu8TfxE7mk7zrdKHJswyqu8pvDkORTHLslVPmoaUyuaz0emkXzVynyZ7nzBchGo1VOdbxd1RN858WGY6txsvBobbUJR+SucwuJpPbCNPJVY2wMWzdoLm7SMvPVgzPDsOU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ideasonboard.com; spf=pass smtp.mailfrom=ideasonboard.com; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b=gDL3HDUp; arc=none smtp.client-ip=213.167.242.64 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="gDL3HDUp" Received: from pendragon.ideasonboard.com (81-175-209-231.bb.dnainternet.fi [81.175.209.231]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 04F88353; Thu, 24 Oct 2024 14:24:53 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1729772694; bh=mKwfBFb98YUVWR1h6VvhXb0DPxsXbBhje3HQ1yKmQao=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=gDL3HDUpPkRR92j2GfhosDCpmJSQsM/mEpIgHA8BBH1ZVP8CJlcQuV63buX1um1n3 SxQaPXw4ubAJtL03L65MZ86FRA5JlmVGTQgA6pSQF/4Yz0oKUr3Tra84mfrfjFbJER w2ShimPws51wWVig6E0+n5oYPF6fOi0tzff+yRGY= Date: Thu, 24 Oct 2024 15:26:36 +0300 From: Laurent Pinchart To: Hans Verkuil Cc: Tomi Valkeinen , Mauro Carvalho Chehab , Raspberry Pi Kernel Maintenance , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Florian Fainelli , Broadcom internal kernel review list , Rob Herring , Krzysztof Kozlowski , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, linux-rpi-kernel@lists.infradead.org, linux-arm-kernel@lists.infradead.org, Naushir Patuck , Sakari Ailus , Jacopo Mondi , Kieran Bingham Subject: Re: [PATCH v6 3/4] media: raspberrypi: Add support for RP1-CFE Message-ID: <20241024122636.GB6081@pendragon.ideasonboard.com> References: <20241003-rp1-cfe-v6-0-d6762edd98a8@ideasonboard.com> <20241003-rp1-cfe-v6-3-d6762edd98a8@ideasonboard.com> <4d9e340e-2ae7-495b-8623-0d10398e1c3d@xs4all.nl> <20241024120507.GA6081@pendragon.ideasonboard.com> <3a5f7d52-fbe9-4592-ab24-50cd6de548c2@xs4all.nl> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <3a5f7d52-fbe9-4592-ab24-50cd6de548c2@xs4all.nl> On Thu, Oct 24, 2024 at 02:13:07PM +0200, Hans Verkuil wrote: > On 24/10/2024 14:05, Laurent Pinchart wrote: > > On Thu, Oct 24, 2024 at 01:21:43PM +0200, Hans Verkuil wrote: > >> On 24/10/2024 13:08, Tomi Valkeinen wrote: > >>> On 24/10/2024 11:20, Hans Verkuil wrote: > >>>> Hi Tomi, > >>>> > >>>> I know this driver is already merged, but while checking for drivers that use > >>>> q->max_num_buffers I stumbled on this cfe code: > >>>> > >>>> > >>>> > >>>>> +/* > >>>>> + * vb2 ops > >>>>> + */ > >>>>> + > >>>>> +static int cfe_queue_setup(struct vb2_queue *vq, unsigned int *nbuffers, > >>>>> +               unsigned int *nplanes, unsigned int sizes[], > >>>>> +               struct device *alloc_devs[]) > >>>>> +{ > >>>>> +    struct cfe_node *node = vb2_get_drv_priv(vq); > >>>>> +    struct cfe_device *cfe = node->cfe; > >>>>> +    unsigned int size = is_image_node(node) ? > >>>>> +                    node->vid_fmt.fmt.pix.sizeimage : > >>>>> +                    node->meta_fmt.fmt.meta.buffersize; > >>>>> + > >>>>> +    cfe_dbg(cfe, "%s: [%s] type:%u\n", __func__, node_desc[node->id].name, > >>>>> +        node->buffer_queue.type); > >>>>> + > >>>>> +    if (vq->max_num_buffers + *nbuffers < 3) > >>>>> +        *nbuffers = 3 - vq->max_num_buffers; > >>>> > >>>> This makes no sense: max_num_buffers is 32, unless explicitly set when vb2_queue_init > >>>> is called. So 32 + *nbuffers is never < 3. > >>>> > >>>> If the idea is that at least 3 buffers should be allocated by REQBUFS, then set > >>>> q->min_reqbufs_allocation = 3; before calling vb2_queue_init and vb2 will handle this > >>>> for you. > >>>> > >>>> Drivers shouldn't modify *nbuffers, except in very rare circumstances, especially > >>>> since the code is almost always wrong. > >>> > >>> Indeed, the code doesn't make sense. I have to say I don't know what > >>> was the intent here, but I think "at least 3 buffers should be > >>> allocated by REQBUFS" is the likely explanation. > >>> > >>> I think the hardware should work with even just a single buffer, so > >>> is it then fine to not set either q->min_queued_buffers nor > >>> q->min_reqbufs_allocation before calling vb2_queue_init()? This > >>> seems to result in REQBUFS giving at least two buffers. > >> > >> min_queued_buffers is really HW dependent. If not set, then > >> start_streaming can be called even if there are no buffers queued. > > > > Having min_queued_buffers > 1 is bad for userspace, and it's much nicer > > to have it set to 0. The main issue with a value of 1 is that validation > > of the pipeline ends up being deferred to the first QBUF if it occurs > > after STREAMON, and error handling is then complicated. > > The validation can be done in the prepare_streaming callback instead of > in start_streaming. prepare_streaming is called at STREAMON time. True, we have that now, I keep forgetting about it. I've noticed the annoying behaviour with drivers that predate .prepare_streaming(). It should be a requirement to validate the pipeline in .prepare_streaming() (or possibly earlier in some cases, not sure). > > It's not just a property of the hardware, kernel drivers can decide to > > work with scratch buffers if needed. In many cases, a scratch buffer > > allocated by the kernel could be very small, either relying on the same > > physical page being mapped through the IOMMU to a larger DMA space, or > > using a 0 stride value to write all lines to the same location. > > None of which is possible for some of the older drivers (e.g. TI davinci) > that do not have an IOMMU and require two contiguous buffers before they can > start streaming. But for modern devices you can solve it through a scratch > buffer, that's true. In the worst case kernel drivers could allocate a full scratch buffer. That's not nice from a memory consumption point of view of course. The stride hack may have worked with TI davinci, I haven't checked. It's something that driver authors don't usually think about even if the hardware can do it. Even if the device supports a 0 stride, it also needs to support programming the stride and the buffer addresses in a race-free way. > > For drivers supported by libcamera, we will require min_queued_buffers > > <= 1 and may tighten that to == 0. Tomi, if you submit a patch, please > > try to target 0, and if that's too much work for now, set it to 1 at > > most. > > Regards, > > Hans > > >> If your hardware can handle that, then it's fine to not set it. > >> > >>>>> + > >>>>> +    if (*nplanes) { > >>>>> +        if (sizes[0] < size) { > >>>>> +            cfe_err(cfe, "sizes[0] %i < size %u\n", sizes[0], size); > >>>>> +            return -EINVAL; > >>>>> +        } > >>>>> +        size = sizes[0]; > >>>>> +    } > >>>>> + > >>>>> +    *nplanes = 1; > >>>>> +    sizes[0] = size; > >>>>> + > >>>>> +    return 0; > >>>>> +} -- Regards, Laurent Pinchart