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Date: Sat, 27 Nov 2021 15:17:51 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: Paul Cercueil <paul@...pouillou.net>
Cc: Alexandru Ardelean <ardeleanalex@...il.com>,
Lars-Peter Clausen <lars@...afoo.de>,
Michael Hennerich <Michael.Hennerich@...log.com>,
Sumit Semwal <sumit.semwal@...aro.org>,
Christian König <christian.koenig@....com>,
linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH 04/15] iio: buffer-dma: Enable buffer write support
On Sun, 21 Nov 2021 17:19:32 +0000
Paul Cercueil <paul@...pouillou.net> wrote:
> Hi Jonathan,
>
> Le dim., nov. 21 2021 at 14:20:49 +0000, Jonathan Cameron
> <jic23@...nel.org> a écrit :
> > On Mon, 15 Nov 2021 14:19:14 +0000
> > Paul Cercueil <paul@...pouillou.net> wrote:
> >
> >> Adding write support to the buffer-dma code is easy - the write()
> >> function basically needs to do the exact same thing as the read()
> >> function: dequeue a block, read or write the data, enqueue the block
> >> when entirely processed.
> >>
> >> Therefore, the iio_buffer_dma_read() and the new
> >> iio_buffer_dma_write()
> >> now both call a function iio_buffer_dma_io(), which will perform
> >> this
> >> task.
> >>
> >> The .space_available() callback can return the exact same value as
> >> the
> >> .data_available() callback for input buffers, since in both cases we
> >> count the exact same thing (the number of bytes in each available
> >> block).
> >>
> >> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
> > Hi Paul,
> >
> > There are a few changes in here, such as the bytes_used value being
> > set that
> > I'm not following the reasoning behind. More info on those?
> > Also good to provide something about those in this patch description.
> >
> > Thanks,
> >
> > Jonathan
> >
> >
> >> ---
> >> drivers/iio/buffer/industrialio-buffer-dma.c | 75
> >> +++++++++++++++-----
> >> include/linux/iio/buffer-dma.h | 7 ++
> >> 2 files changed, 66 insertions(+), 16 deletions(-)
> >>
> >> diff --git a/drivers/iio/buffer/industrialio-buffer-dma.c
> >> b/drivers/iio/buffer/industrialio-buffer-dma.c
> >> index abac88f20104..eeeed6b2e0cf 100644
> >> --- a/drivers/iio/buffer/industrialio-buffer-dma.c
> >> +++ b/drivers/iio/buffer/industrialio-buffer-dma.c
> >> @@ -179,7 +179,8 @@ static struct iio_dma_buffer_block
> >> *iio_dma_buffer_alloc_block(
> >> }
> >>
> >> block->size = size;
> >> - block->state = IIO_BLOCK_STATE_DEQUEUED;
> >> + block->bytes_used = size;
> >> + block->state = IIO_BLOCK_STATE_DONE;
> >
> > I don't know why these are here - some more info?
>
> When using an input buffer the block->bytes_used is unconditionally
> reset in iio_dmaengine_buffer_submit_block(), so this was fine until
> now.
>
> When using an output buffer the block->bytes_used can actually (with
> the new API) be specified by the user, so we don't want
> iio_dmaengine_buffer_submit_block() to unconditionally override it.
> Which means that in the case where we have an output buffer in fileio
> mode, we do need block->bytes_used to be initialized to the buffer's
> size since it won't be set anywhere else.
Makes sense. Thanks for the explanation.
>
> About the change in block->state: in patch [01/15] we removed the
> incoming/outgoing queues, and while the "enqueued" state is still
> useful to know which buffers have to be submitted when the buffer is
> enabled, the "dequeued" state is not useful anymore since there is no
> more distinction vs. the "done" state.
>
> I believe this change should be moved to patch [01/15] then, and I
> should go further and remove the IIO_BLOCK_STATE_DEQUEUED completely.
Complete removal would indeed be a more 'obvious' change, so I'd support
that assuming now disadvantages we havent' thought of yet.
>
> >> block->queue = queue;
> >> INIT_LIST_HEAD(&block->head);
> >> kref_init(&block->kref);
> >> @@ -195,6 +196,18 @@ static void _iio_dma_buffer_block_done(struct
> >> iio_dma_buffer_block *block)
> >> block->state = IIO_BLOCK_STATE_DONE;
> >> }
> >>
> >> +static void iio_dma_buffer_queue_wake(struct iio_dma_buffer_queue
> >> *queue)
> >> +{
> >> + __poll_t flags;
> >> +
> >> + if (queue->buffer.direction == IIO_BUFFER_DIRECTION_IN)
> >> + flags = EPOLLIN | EPOLLRDNORM;
> >> + else
> >> + flags = EPOLLOUT | EPOLLWRNORM;
> >> +
> >> + wake_up_interruptible_poll(&queue->buffer.pollq, flags);
> >> +}
> >> +
> >> /**
> >> * iio_dma_buffer_block_done() - Indicate that a block has been
> >> completed
> >> * @block: The completed block
> >> @@ -212,7 +225,7 @@ void iio_dma_buffer_block_done(struct
> >> iio_dma_buffer_block *block)
> >> spin_unlock_irqrestore(&queue->list_lock, flags);
> >>
> >> iio_buffer_block_put_atomic(block);
> >> - wake_up_interruptible_poll(&queue->buffer.pollq, EPOLLIN |
> >> EPOLLRDNORM);
> >> + iio_dma_buffer_queue_wake(queue);
> >> }
> >> EXPORT_SYMBOL_GPL(iio_dma_buffer_block_done);
> >>
> >> @@ -241,7 +254,7 @@ void iio_dma_buffer_block_list_abort(struct
> >> iio_dma_buffer_queue *queue,
> >> }
> >> spin_unlock_irqrestore(&queue->list_lock, flags);
> >>
> >> - wake_up_interruptible_poll(&queue->buffer.pollq, EPOLLIN |
> >> EPOLLRDNORM);
> >> + iio_dma_buffer_queue_wake(queue);
> >> }
> >> EXPORT_SYMBOL_GPL(iio_dma_buffer_block_list_abort);
> >>
> >> @@ -334,7 +347,8 @@ int iio_dma_buffer_request_update(struct
> >> iio_buffer *buffer)
> >> queue->fileio.blocks[i] = block;
> >> }
> >>
> >> - block->state = IIO_BLOCK_STATE_QUEUED;
> >> + if (queue->buffer.direction == IIO_BUFFER_DIRECTION_IN)
> >> + block->state = IIO_BLOCK_STATE_QUEUED;
> >
> > Possibly worth a comment on the state being set here. I figured it
> > out, but might
> > save some brain cells in future if it's stated in the code.
>
> Ok.
>
> >> }
> >>
> >> out_unlock:
> >> @@ -467,20 +481,12 @@ static struct iio_dma_buffer_block
> >> *iio_dma_buffer_dequeue(
> >> return block;
> >> }
> >>
> >> -/**
> >> - * iio_dma_buffer_read() - DMA buffer read callback
> >> - * @buffer: Buffer to read form
> >> - * @n: Number of bytes to read
> >> - * @user_buffer: Userspace buffer to copy the data to
> >> - *
> >> - * Should be used as the read callback for iio_buffer_access_ops
> >> - * struct for DMA buffers.
> >> - */
> >> -int iio_dma_buffer_read(struct iio_buffer *buffer, size_t n,
> >> - char __user *user_buffer)
> >> +static int iio_dma_buffer_io(struct iio_buffer *buffer,
> >> + size_t n, char __user *user_buffer, bool is_write)
> >> {
> >> struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
> >> struct iio_dma_buffer_block *block;
> >> + void *addr;
> >> int ret;
> >>
> >> if (n < buffer->bytes_per_datum)
> >> @@ -503,8 +509,13 @@ int iio_dma_buffer_read(struct iio_buffer
> >> *buffer, size_t n,
> >> n = rounddown(n, buffer->bytes_per_datum);
> >> if (n > block->bytes_used - queue->fileio.pos)
> >> n = block->bytes_used - queue->fileio.pos;
> >> + addr = block->vaddr + queue->fileio.pos;
> >>
> >> - if (copy_to_user(user_buffer, block->vaddr + queue->fileio.pos,
> >> n)) {
> >> + if (is_write)
> >> + ret = !!copy_from_user(addr, user_buffer, n);
> >> + else
> >> + ret = !!copy_to_user(user_buffer, addr, n);
> >
> > What is the !! gaining us here? We only care about == 0 vs != 0 so
> > forcing it to be 0 or 1 isn't useful.
>
> Right.
>
> >> + if (ret) {
> >> ret = -EFAULT;
> >> goto out_unlock;
> >> }
> >> @@ -513,6 +524,7 @@ int iio_dma_buffer_read(struct iio_buffer
> >> *buffer, size_t n,
> >>
> >> if (queue->fileio.pos == block->bytes_used) {
> >> queue->fileio.active_block = NULL;
> >> + block->bytes_used = block->size;
> >
> > This seems to be a functional change that isn't called out in the
> > patch description.
>
> See the explanation above. Although I most likely don't need to set it
> at two different spots... I'll check that in detail next week.
>
> Cheers,
> -Paul
>
> >> iio_dma_buffer_enqueue(queue, block);
> >> }
> >>
> >> @@ -523,8 +535,39 @@ int iio_dma_buffer_read(struct iio_buffer
> >> *buffer, size_t n,
> >>
> >> return ret;
> >> }
> >> +
> >> +/**
> >> + * iio_dma_buffer_read() - DMA buffer read callback
> >> + * @buffer: Buffer to read form
> >> + * @n: Number of bytes to read
> >> + * @user_buffer: Userspace buffer to copy the data to
> >> + *
> >> + * Should be used as the read callback for iio_buffer_access_ops
> >> + * struct for DMA buffers.
> >> + */
> >> +int iio_dma_buffer_read(struct iio_buffer *buffer, size_t n,
> >> + char __user *user_buffer)
> >> +{
> >> + return iio_dma_buffer_io(buffer, n, user_buffer, false);
> >> +}
> >> EXPORT_SYMBOL_GPL(iio_dma_buffer_read);
> >>
> >> +/**
> >> + * iio_dma_buffer_write() - DMA buffer write callback
> >> + * @buffer: Buffer to read form
> >> + * @n: Number of bytes to read
> >> + * @user_buffer: Userspace buffer to copy the data from
> >> + *
> >> + * Should be used as the write callback for iio_buffer_access_ops
> >> + * struct for DMA buffers.
> >> + */
> >> +int iio_dma_buffer_write(struct iio_buffer *buffer, size_t n,
> >> + const char __user *user_buffer)
> >> +{
> >> + return iio_dma_buffer_io(buffer, n, (__force char *)user_buffer,
> >> true);
> >> +}
> >> +EXPORT_SYMBOL_GPL(iio_dma_buffer_write);
> >> +
> >> /**
> >> * iio_dma_buffer_data_available() - DMA buffer data_available
> >> callback
> >> * @buf: Buffer to check for data availability
> >> diff --git a/include/linux/iio/buffer-dma.h
> >> b/include/linux/iio/buffer-dma.h
> >> index a65a005c4a19..09c07d5563c0 100644
> >> --- a/include/linux/iio/buffer-dma.h
> >> +++ b/include/linux/iio/buffer-dma.h
> >> @@ -132,6 +132,8 @@ int iio_dma_buffer_disable(struct iio_buffer
> >> *buffer,
> >> struct iio_dev *indio_dev);
> >> int iio_dma_buffer_read(struct iio_buffer *buffer, size_t n,
> >> char __user *user_buffer);
> >> +int iio_dma_buffer_write(struct iio_buffer *buffer, size_t n,
> >> + const char __user *user_buffer);
> >> size_t iio_dma_buffer_data_available(struct iio_buffer *buffer);
> >> int iio_dma_buffer_set_bytes_per_datum(struct iio_buffer *buffer,
> >> size_t bpd);
> >> int iio_dma_buffer_set_length(struct iio_buffer *buffer, unsigned
> >> int length);
> >> @@ -142,4 +144,9 @@ int iio_dma_buffer_init(struct
> >> iio_dma_buffer_queue *queue,
> >> void iio_dma_buffer_exit(struct iio_dma_buffer_queue *queue);
> >> void iio_dma_buffer_release(struct iio_dma_buffer_queue *queue);
> >>
> >> +static inline size_t iio_dma_buffer_space_available(struct
> >> iio_buffer *buffer)
> >> +{
> >> + return iio_dma_buffer_data_available(buffer);
> >> +}
> >> +
> >> #endif
> >
>
>
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