Re: [RFCv3 2/2] dma-buf: add helpers for sharing attacher constraints with dma-parms

Marek Szyprowski
2015-02-11T08:28:44Z

Hello,

On 2015-01-27 09:25, Sumit Semwal wrote:
> Add some helpers to share the constraints of devices while attaching
> to the dmabuf buffer.
>
> At each attach, the constraints are calculated based on the following:
> - max_segment_size, max_segment_count, segment_boundary_mask from
> device_dma_parameters.
>
> In case the attaching device's constraints don't match up, attach() fails.
>
> At detach, the constraints are recalculated based on the remaining
> attached devices.
>
> Two helpers are added:
> - dma_buf_get_constraints - which gives the current constraints as calculated
> during each attach on the buffer till the time,
> - dma_buf_recalc_constraints - which recalculates the constraints for all
> currently attached devices for the 'paranoid' ones amongst us.
>
> The idea of this patch is largely taken from Rob Clark's RFC at
> https://lkml.org/lkml/2012/7/19/285, and the comments received on it.
>
> Cc: Rob Clark <robdclark@gmail.com>
> Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>

The code looks okay, although it will probably will work well only with
typical
cases like 'contiguous memory needed' or 'no constraints at all' (iommu).

Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>

> ---
> v3:
> - Thanks to Russell's comment, remove dma_mask and coherent_dma_mask from
> constraints' calculation; has a nice side effect of letting us use
> device_dma_parameters directly to list constraints.
> - update the debugfs output to show constraint info as well.
>
> v2: split constraints-sharing and allocation helpers
>
> drivers/dma-buf/dma-buf.c | 126 +++++++++++++++++++++++++++++++++++++++++++++-
> include/linux/dma-buf.h | 7 +++
> 2 files changed, 132 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 5be225c2ba98..f363f1440803 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -264,6 +264,66 @@ static inline int is_dma_buf_file(struct file *file)
> return file->f_op == &dma_buf_fops;
> }
>
> +static inline void init_constraints(struct device_dma_parameters *cons)
> +{
> + cons->max_segment_count = (unsigned int)-1;
> + cons->max_segment_size = (unsigned int)-1;
> + cons->segment_boundary_mask = (unsigned long)-1;
> +}
> +
> +/*
> + * calc_constraints - calculates if the new attaching device's constraints
> + * match, with the constraints of already attached devices; if yes, returns
> + * the constraints; else return ERR_PTR(-EINVAL)
> + */
> +static int calc_constraints(struct device *dev,
> + struct device_dma_parameters *calc_cons)
> +{
> + struct device_dma_parameters cons = *calc_cons;
> +
> + cons.max_segment_count = min(cons.max_segment_count,
> + dma_get_max_seg_count(dev));
> + cons.max_segment_size = min(cons.max_segment_size,
> + dma_get_max_seg_size(dev));
> + cons.segment_boundary_mask &= dma_get_seg_boundary(dev);
> +
> + if (!cons.max_segment_count ||
> + !cons.max_segment_size ||
> + !cons.segment_boundary_mask) {
> + pr_err("Dev: %s's constraints don't match\n", dev_name(dev));
> + return -EINVAL;
> + }
> +
> + *calc_cons = cons;
> +
> + return 0;
> +}
> +
> +/*
> + * recalc_constraints - recalculates constraints for all attached devices;
> + * useful for detach() recalculation, and for dma_buf_recalc_constraints()
> + * helper.
> + * Returns recalculated constraints in recalc_cons, or error in the unlikely
> + * case when constraints of attached devices might have changed.
> + */
> +static int recalc_constraints(struct dma_buf *dmabuf,
> + struct device_dma_parameters *recalc_cons)
> +{
> + struct device_dma_parameters calc_cons;
> + struct dma_buf_attachment *attach;
> + int ret = 0;
> +
> + init_constraints(&calc_cons);
> +
> + list_for_each_entry(attach, &dmabuf->attachments, node) {
> + ret = calc_constraints(attach->dev, &calc_cons);
> + if (ret)
> + return ret;
> + }
> + *recalc_cons = calc_cons;
> + return 0;
> +}
> +
> /**
> * dma_buf_export_named - Creates a new dma_buf, and associates an anon file
> * with this buffer, so it can be exported.
> @@ -313,6 +373,9 @@ struct dma_buf *dma_buf_export_named(void *priv, const struct dma_buf_ops *ops,
> dmabuf->ops = ops;
> dmabuf->size = size;
> dmabuf->exp_name = exp_name;
> +
> + init_constraints(&dmabuf->constraints);
> +
> init_waitqueue_head(&dmabuf->poll);
> dmabuf->cb_excl.poll = dmabuf->cb_shared.poll = &dmabuf->poll;
> dmabuf->cb_excl.active = dmabuf->cb_shared.active = 0;
> @@ -422,7 +485,7 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
> struct device *dev)
> {
> struct dma_buf_attachment *attach;
> - int ret;
> + int ret = 0;
>
> if (WARN_ON(!dmabuf || !dev))
> return ERR_PTR(-EINVAL);
> @@ -436,6 +499,9 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
>
> mutex_lock(&dmabuf->lock);
>
> + if (calc_constraints(dev, &dmabuf->constraints))
> + goto err_constraints;
> +
> if (dmabuf->ops->attach) {
> ret = dmabuf->ops->attach(dmabuf, dev, attach);
> if (ret)
> @@ -448,6 +514,7 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
>
> err_attach:
> kfree(attach);
> +err_constraints:
> mutex_unlock(&dmabuf->lock);
> return ERR_PTR(ret);
> }
> @@ -470,6 +537,8 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
> if (dmabuf->ops->detach)
> dmabuf->ops->detach(dmabuf, attach);
>
> + recalc_constraints(dmabuf, &dmabuf->constraints);
> +
> mutex_unlock(&dmabuf->lock);
> kfree(attach);
> }
> @@ -770,6 +839,56 @@ void dma_buf_vunmap(struct dma_buf *dmabuf, void *vaddr)
> }
> EXPORT_SYMBOL_GPL(dma_buf_vunmap);
>
> +/**
> + * dma_buf_get_constraints - get the *current* constraints of the dmabuf,
> + * as calculated during each attach(); returns error on invalid inputs
> + *
> + * @dmabuf: [in] buffer to get constraints of
> + * @constraints: [out] current constraints are returned in this
> + */
> +int dma_buf_get_constraints(struct dma_buf *dmabuf,
> + struct device_dma_parameters *constraints)
> +{
> + if (WARN_ON(!dmabuf || !constraints))
> + return -EINVAL;
> +
> + mutex_lock(&dmabuf->lock);
> + *constraints = dmabuf->constraints;
> + mutex_unlock(&dmabuf->lock);
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_get_constraints);
> +
> +/**
> + * dma_buf_recalc_constraints - *recalculate* the constraints for the buffer
> + * afresh, from the list of currently attached devices; this could be useful
> + * cross-check the current constraints, for exporters that might want to be
> + * 'paranoid' about the device constraints.
> + *
> + * returns error on invalid inputs
> + *
> + * @dmabuf: [in] buffer to get constraints of
> + * @constraints: [out] recalculated constraints are returned in this
> + */
> +int dma_buf_recalc_constraints(struct dma_buf *dmabuf,
> + struct device_dma_parameters *constraints)
> +{
> + struct device_dma_parameters calc_cons;
> + int ret = 0;
> +
> + if (WARN_ON(!dmabuf || !constraints))
> + return -EINVAL;
> +
> + mutex_lock(&dmabuf->lock);
> + ret = recalc_constraints(dmabuf, &calc_cons);
> + if (!ret)
> + *constraints = calc_cons;
> +
> + mutex_unlock(&dmabuf->lock);
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_recalc_constraints);
> +
> #ifdef CONFIG_DEBUG_FS
> static int dma_buf_describe(struct seq_file *s)
> {
> @@ -801,6 +920,11 @@ static int dma_buf_describe(struct seq_file *s)
> buf_obj->file->f_flags, buf_obj->file->f_mode,
> file_count(buf_obj->file),
> buf_obj->exp_name);
> + seq_printf(s, "\tConstraints: Seg Count: %08u, Seg Size: %08u",
> + buf_obj->constraints.max_segment_count,
> + buf_obj->constraints.max_segment_size);
> + seq_printf(s, " seg boundary mask: %08lx\n",
> + buf_obj->constraints.segment_boundary_mask);
>
> seq_puts(s, "\tAttached Devices:\n");
> attach_count = 0;
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index 694e1fe1c4b4..489ad9b2e5ae 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -34,6 +34,7 @@
> #include <linux/wait.h>
>
> struct device;
> +struct device_dma_parameters;
> struct dma_buf;
> struct dma_buf_attachment;
>
> @@ -116,6 +117,7 @@ struct dma_buf_ops {
> * @ops: dma_buf_ops associated with this buffer object.
> * @exp_name: name of the exporter; useful for debugging.
> * @list_node: node for dma_buf accounting and debugging.
> + * @constraints: calculated constraints of attached devices.
> * @priv: exporter specific private data for this buffer object.
> * @resv: reservation object linked to this dma-buf
> */
> @@ -130,6 +132,7 @@ struct dma_buf {
> void *vmap_ptr;
> const char *exp_name;
> struct list_head list_node;
> + struct device_dma_parameters constraints;
> void *priv;
> struct reservation_object *resv;
>
> @@ -211,4 +214,8 @@ void *dma_buf_vmap(struct dma_buf *);
> void dma_buf_vunmap(struct dma_buf *, void *vaddr);
> int dma_buf_debugfs_create_file(const char *name,
> int (*write)(struct seq_file *));
> +
> +int dma_buf_get_constraints(struct dma_buf *, struct device_dma_parameters *);
> +int dma_buf_recalc_constraints(struct dma_buf *,
> + struct device_dma_parameters *);
> #endif /* __DMA_BUF_H__ */

Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland