Re: [PATCH 07/12] lib/igt_kms: Add support for the OUT_FENCE_PTR property

[Brian Starkey <brian.starkey@arm.com>]

On Tue, Nov 22, 2016 at 11:06:00AM +0000, Chris Wilson wrote:
>On Tue, Nov 22, 2016 at 10:53:51AM +0000, Brian Starkey wrote:
>> Hi Gustavo,
>>
>> A little late to the party here, but I was blocked by our internal
>> contributions process...
>>
>> I didn't see these end up in my checkout yet though, so I guess they
>> aren't picked up yet.
>>
>> On Mon, Nov 14, 2016 at 06:59:21PM +0900, Gustavo Padovan wrote:
>> >From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
>> >
>> >Add support for the OUT_FENCE_PTR property to enable setting out fences for
>> >atomic commits.
>> >
>> >Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
>> >---
>> >lib/igt_kms.c | 20 +++++++++++++++++++-
>> >lib/igt_kms.h |  3 +++
>> >2 files changed, 22 insertions(+), 1 deletion(-)
>> >
>> >diff --git a/lib/igt_kms.c b/lib/igt_kms.c
>> >index 4748c0a..f25e1eb 100644
>> >--- a/lib/igt_kms.c
>> >+++ b/lib/igt_kms.c
>> >@@ -175,7 +175,8 @@ const char *igt_crtc_prop_names[IGT_NUM_CRTC_PROPS] = {
>> >	"DEGAMMA_LUT",
>> >	"GAMMA_LUT",
>> >	"MODE_ID",
>> >-	"ACTIVE"
>> >+	"ACTIVE",
>> >+	"OUT_FENCE_PTR"
>> >};
>> >
>> >const char *igt_connector_prop_names[IGT_NUM_CONNECTOR_PROPS] = {
>> >@@ -2103,6 +2104,9 @@ static void igt_atomic_prepare_crtc_commit(igt_pipe_t *pipe_obj, drmModeAtomicRe
>> >		igt_atomic_populate_crtc_req(req, pipe_obj, IGT_CRTC_ACTIVE, !!output);
>> >	}
>> >
>> >+	if (pipe_obj->out_fence_ptr)
>> >+		igt_atomic_populate_crtc_req(req, pipe_obj, IGT_CRTC_OUT_FENCE_PTR, pipe_obj->out_fence_ptr);
>> >+
>> >	/*
>> >	 *	TODO: Add all crtc level properties here
>> >	 */
>> >@@ -2683,6 +2687,20 @@ igt_pipe_set_gamma_lut(igt_pipe_t *pipe, void *ptr, size_t length)
>> >}
>> >
>> >/**
>> >+ * igt_pipe_set_out_fence_ptr:
>> >+ * @pipe: pipe pointer to which background color to be set
>> >+ * @fence_ptr: out fence pointer
>>
>> I don't think fence_ptr can be int *. It needs to be a pointer to a
>> 64-bit type.
>>
>> >+ *
>> >+ * Sets the out fence pointer that will be passed to the kernel in
>> >+ * the atomic ioctl. When the kernel returns the out fence pointer
>> >+ * will contain the fd number of the out fence created by KMS.
>> >+ */
>> >+void igt_pipe_set_out_fence_ptr(igt_pipe_t *pipe, int *fence_ptr)
>> >+{
>> >+	pipe->out_fence_ptr = (uint64_t) fence_ptr;
>> >+}
>> >+
>> >+/**
>> > * igt_crtc_set_background:
>> > * @pipe: pipe pointer to which background color to be set
>> > * @background: background color value in BGR 16bpc
>> >diff --git a/lib/igt_kms.h b/lib/igt_kms.h
>> >index 344f931..02d7bd1 100644
>> >--- a/lib/igt_kms.h
>> >+++ b/lib/igt_kms.h
>> >@@ -110,6 +110,7 @@ enum igt_atomic_crtc_properties {
>> >       IGT_CRTC_GAMMA_LUT,
>> >       IGT_CRTC_MODE_ID,
>> >       IGT_CRTC_ACTIVE,
>> >+       IGT_CRTC_OUT_FENCE_PTR,
>> >       IGT_NUM_CRTC_PROPS
>> >};
>> >
>> >@@ -298,6 +299,7 @@ struct igt_pipe {
>> >
>> >	uint64_t mode_blob;
>> >	bool mode_changed;
>> >+	uint64_t out_fence_ptr;
>>
>> IMO this should be:
>>
>> 	int64_t *out_fence_ptr;
>
>In userspace, fences are *fd*, a plain int. It is only the uabi that we
>pass pointers as u64 to the kernel, and indeed that should be limited to
>the uabi wrapper.
>-Chris

Where's the uabi wrapper in this case?

Wherever it is, afaik someone needs to have 64-bit type for the kernel
to stash its fd in - on the kernel side out_fence_ptr is
(s64 __user *), so if there's not a 64-bit variable on the other end
of it then someone's going to have a bad day.

-Brian

>
>-- 
>Chris Wilson, Intel Open Source Technology Centre
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