linux-kernel - Re: [PATCH v2 10/10] drm/msm: Add a way for userspace to allocate GPU iova

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Message-ID: <ad97096f-cc90-4f20-0f73-f33e9b275f1a@collabora.com>
Date:   Thu, 31 Mar 2022 21:52:11 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Rob Clark <robdclark@...il.com>, dri-devel@...ts.freedesktop.org
Cc:     freedreno@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Rob Clark <robdclark@...omium.org>,
        Sean Paul <sean@...rly.run>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Akhil P Oommen <quic_akhilpo@...cinc.com>,
        Jonathan Marek <jonathan@...ek.ca>,
        Jordan Crouse <jordan@...micpenguin.net>,
        Emma Anholt <emma@...olt.net>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 10/10] drm/msm: Add a way for userspace to allocate GPU
 iova

...
> +/*
> + * Get the requested iova but don't pin it.  Fails if the requested iova is
> + * not available.  Doesn't need a put because iovas are currently valid for
> + * the life of the object.
> + *
> + * Setting an iova of zero will clear the vma.
> + */
> +int msm_gem_set_iova(struct drm_gem_object *obj,
> +		     struct msm_gem_address_space *aspace, uint64_t iova)
> +{
> +	int ret = 0;

nit: No need to initialize the ret

> +	msm_gem_lock(obj);
> +	if (!iova) {
> +		ret = clear_iova(obj, aspace);
> +	} else {
> +		struct msm_gem_vma *vma;
> +		vma = get_vma_locked(obj, aspace, iova, iova + obj->size);
> +		if (IS_ERR(vma)) {
> +			ret = PTR_ERR(vma);
> +		} else if (GEM_WARN_ON(vma->iova != iova)) {
> +			clear_iova(obj, aspace);
> +			ret = -ENOSPC;

The (vma->iova != iova) means that vma is already set, but to a
different address. Is -ENOSPC really appropriate here? -EBUSY or -EINVAL
looks more natural to me.

> +		}
> +	}
> +	msm_gem_unlock(obj);
> +
> +	return ret;
> +}
> +
>  /*
>   * Unpin a iova by updating the reference counts. The memory isn't actually
>   * purged until something else (shrinker, mm_notifier, destroy, etc) decides
> diff --git a/drivers/gpu/drm/msm/msm_gem.h b/drivers/gpu/drm/msm/msm_gem.h
> index 38d66e1248b1..efa2e5c19f1e 100644
> --- a/drivers/gpu/drm/msm/msm_gem.h
> +++ b/drivers/gpu/drm/msm/msm_gem.h
> @@ -38,6 +38,12 @@ struct msm_gem_address_space {
>  
>  	/* @faults: the number of GPU hangs associated with this address space */
>  	int faults;
> +
> +	/** @va_start: lowest possible address to allocate */
> +	uint64_t va_start;
> +
> +	/** @va_size: the size of the address space (in bytes) */
> +	uint64_t va_size;
>  };
>  
>  struct msm_gem_address_space *
> @@ -144,6 +150,8 @@ struct msm_gem_vma *msm_gem_get_vma_locked(struct drm_gem_object *obj,
>  					   struct msm_gem_address_space *aspace);
>  int msm_gem_get_iova(struct drm_gem_object *obj,
>  		struct msm_gem_address_space *aspace, uint64_t *iova);
> +int msm_gem_set_iova(struct drm_gem_object *obj,
> +		struct msm_gem_address_space *aspace, uint64_t iova);
>  int msm_gem_get_and_pin_iova_range(struct drm_gem_object *obj,
>  		struct msm_gem_address_space *aspace, uint64_t *iova,
>  		u64 range_start, u64 range_end);
nit: There is an odd mix of uint64_t and u64 (and alike) in the MSM code
:) The uint64_t variant shouldn't be used by kernel code in general and
checkpatch should want about it.