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SubjectRe: [PATCH v3] spi: spi-ep93xx: Use dma_data_direction for ep93xx_spi_dma_{finish,prepare}
Nathan,
Thanks for your patience and continued support working towards an
optimal solution to fix this warning. Some thoughts below.

On Fri, Oct 5, 2018 at 12:29 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> Clang warns when one enumerated type is implicitly converted to another.
>
> drivers/spi/spi-ep93xx.c:342:62: warning: implicit conversion from
> enumeration type 'enum dma_transfer_direction' to different enumeration
> type 'enum dma_data_direction' [-Wenum-conversion]
> nents = dma_map_sg(chan->device->dev, sgt->sgl, sgt->nents, dir);
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~
> ./include/linux/dma-mapping.h:428:58: note: expanded from macro
> 'dma_map_sg'
> #define dma_map_sg(d, s, n, r) dma_map_sg_attrs(d, s, n, r, 0)
> ~~~~~~~~~~~~~~~~ ^
> drivers/spi/spi-ep93xx.c:348:57: warning: implicit conversion from
> enumeration type 'enum dma_transfer_direction' to different enumeration
> type 'enum dma_data_direction' [-Wenum-conversion]
> dma_unmap_sg(chan->device->dev, sgt->sgl, sgt->nents, dir);
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~
> ./include/linux/dma-mapping.h:429:62: note: expanded from macro
> 'dma_unmap_sg'
> #define dma_unmap_sg(d, s, n, r) dma_unmap_sg_attrs(d, s, n, r, 0)
> ~~~~~~~~~~~~~~~~~~ ^
> drivers/spi/spi-ep93xx.c:377:56: warning: implicit conversion from
> enumeration type 'enum dma_transfer_direction' to different enumeration
> type 'enum dma_data_direction' [-Wenum-conversion]
> dma_unmap_sg(chan->device->dev, sgt->sgl, sgt->nents, dir);
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~
> ./include/linux/dma-mapping.h:429:62: note: expanded from macro
> 'dma_unmap_sg'
> #define dma_unmap_sg(d, s, n, r) dma_unmap_sg_attrs(d, s, n, r, 0)
> ~~~~~~~~~~~~~~~~~~ ^
> 3 warnings generated.
>
> dma_{,un}map_sg expect an enum of type dma_data_direction but this
> driver uses dma_transfer_direction for everything. Convert the driver to
> use dma_data_direction for these two functions.
>
> There are two places that strictly require an enum of type
> dma_transfer_direction: the direction member in struct dma_slave_config
> and the direction parameter in dmaengine_prep_slave_sg. To avoid using
> an explicit cast, add a simple function, ep93xx_dma_data_to_trans_dir,
> to safely map between the two types because they are not 1 to 1 in
> meaning.
>
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> ---
>
> v1 -> v2:
>
> * Fix escaped hash symbols for '#define' lines (\# -> #)
>
> v2 -> v3:
>
> * Instead of changing the dir parameter in the prepare and finish
> functions, convert the driver to use dma_data_direction for everywhere
> that makes sense. Add a helper function to convert between the two
> types as there is still a couple of locations that need a transfer
> enum (and no such function exists). Alternatively, the function could
> just convert from transfer -> data and be used in dma_{,un}map_sg and
> the rest of the driver be left alone. Hopefully I understood what Mika
> wanted!
>
> drivers/spi/spi-ep93xx.c | 37 ++++++++++++++++++++++++++-----------
> 1 file changed, 26 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/spi/spi-ep93xx.c b/drivers/spi/spi-ep93xx.c
> index f1526757aaf6..667da7964d63 100644
> --- a/drivers/spi/spi-ep93xx.c
> +++ b/drivers/spi/spi-ep93xx.c
> @@ -246,6 +246,19 @@ static int ep93xx_spi_read_write(struct spi_master *master)
> return -EINPROGRESS;
> }
>
> +static enum dma_transfer_direction
> +ep93xx_dma_data_to_trans_dir(enum dma_data_direction dir)
> +{
> + switch (dir) {
> + case DMA_TO_DEVICE:
> + return DMA_MEM_TO_DEV;
> + case DMA_FROM_DEVICE:
> + return DMA_DEV_TO_MEM;
> + default:
> + return DMA_TRANS_NONE;
> + }
> +}
> +
> /**
> * ep93xx_spi_dma_prepare() - prepares a DMA transfer
> * @master: SPI master
> @@ -257,7 +270,7 @@ static int ep93xx_spi_read_write(struct spi_master *master)
> */
> static struct dma_async_tx_descriptor *
> ep93xx_spi_dma_prepare(struct spi_master *master,
> - enum dma_transfer_direction dir)
> + enum dma_data_direction dir)
> {
> struct ep93xx_spi *espi = spi_master_get_devdata(master);
> struct spi_transfer *xfer = master->cur_msg->state;
> @@ -277,9 +290,9 @@ ep93xx_spi_dma_prepare(struct spi_master *master,
> buswidth = DMA_SLAVE_BUSWIDTH_1_BYTE;
>
> memset(&conf, 0, sizeof(conf));
> - conf.direction = dir;
> + conf.direction = ep93xx_dma_data_to_trans_dir(dir);
>
> - if (dir == DMA_DEV_TO_MEM) {
> + if (dir == DMA_FROM_DEVICE) {
> chan = espi->dma_rx;
> buf = xfer->rx_buf;
> sgt = &espi->rx_sgt;
> @@ -343,7 +356,9 @@ ep93xx_spi_dma_prepare(struct spi_master *master,
> if (!nents)
> return ERR_PTR(-ENOMEM);
>
> - txd = dmaengine_prep_slave_sg(chan, sgt->sgl, nents, dir, DMA_CTRL_ACK);
> + txd = dmaengine_prep_slave_sg(chan, sgt->sgl, nents,
> + ep93xx_dma_data_to_trans_dir(dir),

So we've already calculated this once already in this function, and
the value of `dir` hasn't changed since. While the compiler might be
able to optimize out this common sub expression (CSE or GVN I think
are the compiler passes that could optimize this out), I think it
would be better to guarantee that this precalculated value is always
used by replacing the rematerialization of the value
(`ep93xx_dma_data_to_trans_dir(dir)`) with `conf.direction`.

> + DMA_CTRL_ACK);
> if (!txd) {
> dma_unmap_sg(chan->device->dev, sgt->sgl, sgt->nents, dir);
> return ERR_PTR(-ENOMEM);
> @@ -360,13 +375,13 @@ ep93xx_spi_dma_prepare(struct spi_master *master,
> * unmapped.
> */
> static void ep93xx_spi_dma_finish(struct spi_master *master,
> - enum dma_transfer_direction dir)
> + enum dma_data_direction dir)
> {
> struct ep93xx_spi *espi = spi_master_get_devdata(master);
> struct dma_chan *chan;
> struct sg_table *sgt;
>
> - if (dir == DMA_DEV_TO_MEM) {
> + if (dir == DMA_FROM_DEVICE) {
> chan = espi->dma_rx;
> sgt = &espi->rx_sgt;
> } else {
> @@ -381,8 +396,8 @@ static void ep93xx_spi_dma_callback(void *callback_param)
> {
> struct spi_master *master = callback_param;
>
> - ep93xx_spi_dma_finish(master, DMA_MEM_TO_DEV);
> - ep93xx_spi_dma_finish(master, DMA_DEV_TO_MEM);
> + ep93xx_spi_dma_finish(master, DMA_TO_DEVICE);
> + ep93xx_spi_dma_finish(master, DMA_FROM_DEVICE);
>
> spi_finalize_current_transfer(master);
> }
> @@ -392,15 +407,15 @@ static int ep93xx_spi_dma_transfer(struct spi_master *master)
> struct ep93xx_spi *espi = spi_master_get_devdata(master);
> struct dma_async_tx_descriptor *rxd, *txd;
>
> - rxd = ep93xx_spi_dma_prepare(master, DMA_DEV_TO_MEM);
> + rxd = ep93xx_spi_dma_prepare(master, DMA_FROM_DEVICE);
> if (IS_ERR(rxd)) {
> dev_err(&master->dev, "DMA RX failed: %ld\n", PTR_ERR(rxd));
> return PTR_ERR(rxd);
> }
>
> - txd = ep93xx_spi_dma_prepare(master, DMA_MEM_TO_DEV);
> + txd = ep93xx_spi_dma_prepare(master, DMA_TO_DEVICE);
> if (IS_ERR(txd)) {
> - ep93xx_spi_dma_finish(master, DMA_DEV_TO_MEM);
> + ep93xx_spi_dma_finish(master, DMA_FROM_DEVICE);
> dev_err(&master->dev, "DMA TX failed: %ld\n", PTR_ERR(txd));
> return PTR_ERR(txd);
> }
> --
> 2.19.0
>


--
Thanks,
~Nick Desaulniers

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