Hi Rusty,
> From: Rusty Russell [mailto:ru...@rustcorp.com.au]
> sjur.brandel...@stericsson.com writes:
> > From: Vikram ARV <vikram....@stericsson.com>
> >
> > Add the the Virtio shared memory driver for STE Modems.
> > caif_virtio is implemented utilizing the virtio framework
> > for data transport and is managed with the remoteproc frameworks.
> >
> > The Virtio queue is used for transmitting data to the modem, and
> > the new vringh implementation is receiving data over the vring.
>
> OK, let's refine vringh now we can see another user:
>
> > + * @head: Last descriptor ID we received from vringh_getdesc_kern.
> > + * We use this to put descriptor back on the used ring. USHRT_MAX is
> > + * used to indicate invalid head-id.
>
> > + */
> > +struct cfv_napi_context {
> > + struct vringh_kiov riov;
> > + unsigned short head;
> > +};
>
> Usually we use an int, and -1. I imagine it'll take no more space,
> due to padding.
I'm passing a pointer to "head" to vringh_getdesc_kern() directly, are you
suggesting to change the head argument in vringh_getdesc_kern()
to a int pointer as well then?
> > +static inline void ctx_prep_iov(struct cfv_napi_context *ctx)
> > +{
> > + if (ctx->riov.allocated) {
> > + kfree(ctx->riov.iov);
> > + ctx->riov.iov = NULL;
> > + ctx->riov.allocated = false;
> > + }
> > + ctx->riov.iov = NULL;
> > + ctx->riov.i = 0;
> > + ctx->riov.max = 0;
> > +}
>
> Hmm, we should probably make sure you don't have to do this: that if
> allocated once, you can simply reuse it by setting i = 0.
Yes, I had problems getting the alloc/free of iov right. This is
perhaps the least intuitively part of the API. I maybe it's just me, but
I think some more helper functions and support from vringh in this
area would be great.
>
> (This requires some care in the error handling paths, so we don't
> free it from under you)...
>
> And you probably want to free this up in cfv_remove() instead?
OK, I'll look into this when you have a some more code ready...
>
> I'll create and test a patch now.
>
> > + if (riov->i == riov->max) {
> > + if (cfv->ctx.head != USHRT_MAX) {
> > + vringh_complete_kern(cfv->vr_rx,
> > + cfv->ctx.head,
> > + 0);
> > + cfv->ctx.head = USHRT_MAX;
> > + }
> > +
> > + ctx_prep_iov(&cfv->ctx);
> > + err = vringh_getdesc_kern(
> > + cfv->vr_rx,
> > + riov,
> > + &wiov,
> > + &cfv->ctx.head,
> > + GFP_ATOMIC);
> > +
> > + if (err <= 0)
> > + goto out;
> > +
> > + if (wiov.max != 0) {
> > + /* CAIF does not use write descriptors */
> > + err = -EPROTO;
> > + goto out;
> > + }
>
> This is probably a common case, so we should generate this error inside
> vringh_getdesc (if wiov is NULL).
>
> I'll do that too...
>
> > +module_driver(caif_virtio_driver, register_virtio_driver,
> > + unregister_virtio_driver);
> > +MODULE_DEVICE_TABLE(virtio, id_table);
>
> The comment on module_driver says:
>
> * Use this macro to construct bus specific macros for registering
> * drivers, and do not use it on its own.
>
> Want to send me a patch to define module_virtio_driver?
Sure, I can do that.
Thanks a lot Rusty.
Regards,
Sjur
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