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    SubjectRe: [PATCH 08/11] dmaengine: xilinx_dpdma: stop using slave_id field
    Hi Arnd,

    Thank you for the patch.

    On Mon, Nov 15, 2021 at 09:54:00AM +0100, Arnd Bergmann wrote:
    > From: Arnd Bergmann <arnd@arndb.de>
    >
    > The display driver wants to pass a custom flag to the DMA engine driver,
    > which it started doing by using the slave_id field that was traditionally
    > used for a different purpose.
    >
    > As there is no longer a correct use for the slave_id field, it should
    > really be removed, and the remaining users changed over to something
    > different.
    >
    > The new mechanism for passing nonstandard settings is using the
    > .peripheral_config field, so use that to pass a newly defined structure
    > here, making it clear that this will not work in portable drivers.
    >
    > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
    > ---
    > drivers/dma/xilinx/xilinx_dpdma.c | 12 ++++++++----
    > drivers/gpu/drm/xlnx/zynqmp_disp.c | 9 +++++++--
    > include/linux/dma/xilinx_dpdma.h | 11 +++++++++++
    > 3 files changed, 26 insertions(+), 6 deletions(-)
    > create mode 100644 include/linux/dma/xilinx_dpdma.h
    >
    > diff --git a/drivers/dma/xilinx/xilinx_dpdma.c b/drivers/dma/xilinx/xilinx_dpdma.c
    > index ce5c66e6897d..e2c1ef7a659c 100644
    > --- a/drivers/dma/xilinx/xilinx_dpdma.c
    > +++ b/drivers/dma/xilinx/xilinx_dpdma.c
    > @@ -12,6 +12,7 @@
    > #include <linux/clk.h>
    > #include <linux/debugfs.h>
    > #include <linux/delay.h>
    > +#include <linux/dma/xilinx_dpdma.h>
    > #include <linux/dmaengine.h>
    > #include <linux/dmapool.h>
    > #include <linux/interrupt.h>
    > @@ -1273,6 +1274,7 @@ static int xilinx_dpdma_config(struct dma_chan *dchan,
    > struct dma_slave_config *config)
    > {
    > struct xilinx_dpdma_chan *chan = to_xilinx_chan(dchan);
    > + struct xilinx_dpdma_peripheral_config *pconfig;
    > unsigned long flags;
    >
    > /*
    > @@ -1285,11 +1287,13 @@ static int xilinx_dpdma_config(struct dma_chan *dchan,
    > spin_lock_irqsave(&chan->lock, flags);
    >
    > /*
    > - * Abuse the slave_id to indicate that the channel is part of a video
    > - * group.
    > + * Abuse the peripheral_config to indicate that the channel is part

    Is it still an abuse, or is this now the right way to pass custom data
    to the DMA engine driver ?

    > + * of a video group.
    > */
    > - if (chan->id <= ZYNQMP_DPDMA_VIDEO2)
    > - chan->video_group = config->slave_id != 0;
    > + pconfig = config->peripheral_config;

    This could be moved to the variable declaration above, up to you.

    > + if (chan->id <= ZYNQMP_DPDMA_VIDEO2 &&
    > + config->peripheral_size == sizeof(*pconfig))

    Silently ignoring a size mismatch isn't nice. Could we validate the size
    at the beginning of the function and return an error ?

    With these issues addressed,

    Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

    > + chan->video_group = pconfig->video_group;
    >
    > spin_unlock_irqrestore(&chan->lock, flags);
    >
    > diff --git a/drivers/gpu/drm/xlnx/zynqmp_disp.c b/drivers/gpu/drm/xlnx/zynqmp_disp.c
    > index ff2b308d8651..11c409cbc88e 100644
    > --- a/drivers/gpu/drm/xlnx/zynqmp_disp.c
    > +++ b/drivers/gpu/drm/xlnx/zynqmp_disp.c
    > @@ -24,6 +24,7 @@
    >
    > #include <linux/clk.h>
    > #include <linux/delay.h>
    > +#include <linux/dma/xilinx_dpdma.h>
    > #include <linux/dma-mapping.h>
    > #include <linux/dmaengine.h>
    > #include <linux/module.h>
    > @@ -1058,14 +1059,18 @@ static void zynqmp_disp_layer_set_format(struct zynqmp_disp_layer *layer,
    > zynqmp_disp_avbuf_set_format(layer->disp, layer, layer->disp_fmt);
    >
    > /*
    > - * Set slave_id for each DMA channel to indicate they're part of a
    > + * Set pconfig for each DMA channel to indicate they're part of a
    > * video group.
    > */
    > for (i = 0; i < info->num_planes; i++) {
    > struct zynqmp_disp_layer_dma *dma = &layer->dmas[i];
    > + struct xilinx_dpdma_peripheral_config pconfig = {
    > + .video_group = true,
    > + };
    > struct dma_slave_config config = {
    > .direction = DMA_MEM_TO_DEV,
    > - .slave_id = 1,
    > + .peripheral_config = &pconfig,
    > + .peripheral_size = sizeof(pconfig),
    > };
    >
    > dmaengine_slave_config(dma->chan, &config);
    > diff --git a/include/linux/dma/xilinx_dpdma.h b/include/linux/dma/xilinx_dpdma.h
    > new file mode 100644
    > index 000000000000..83a1377f03f8
    > --- /dev/null
    > +++ b/include/linux/dma/xilinx_dpdma.h
    > @@ -0,0 +1,11 @@
    > +// SPDX-License-Identifier: GPL-2.0
    > +#ifndef __LINUX_DMA_XILINX_DPDMA_H
    > +#define __LINUX_DMA_XILINX_DPDMA_H
    > +
    > +#include <linux/types.h>
    > +
    > +struct xilinx_dpdma_peripheral_config {
    > + bool video_group;
    > +};
    > +
    > +#endif /* __LINUX_DMA_XILINX_DPDMA_H */

    --
    Regards,

    Laurent Pinchart

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