Re: [PATCH] drm/bridge/synopsys: dsi: use common mipi_dsi_create_packet()

[Brian Norris <briannorris@chromium.org>]

Hi Philippe,

On Tue, Jan 09, 2018 at 10:48:43AM +0000, Philippe CORNU wrote:
> Hi Brian,
> 
> And many thanks for implementing these TODOs.

And thanks for adding them; it gave me a better option than just adding
yet another switch case (MIPI_DSI_GENERIC_LONG_WRITE) ;)

> On 01/06/2018 01:38 AM, Brian Norris wrote:
> > This takes care of 2 TODOs in this driver, by using the common DSI
> > packet-marshalling code instead of our custom short/long write code.
> > This both saves us some duplicated code and gets us free support for
> > command types that weren't already part of our switch block (e.g.,
> > MIPI_DSI_GENERIC_LONG_WRITE).
> > 
> > The code logic stays mostly intact, except that it becomes unnecessary
> > to split the short/long write functions, and we have to copy data a bit
> > more.
> > 
> > Along the way, I noticed that loop bounds were a little odd:
> > 
> > 	while (DIV_ROUND_UP(len, pld_data_bytes))
> > 
> > This really was just supposed to be 'len != 0', so I made that more
> > clear.
> > 
> > Tested on RK3399 with some pending refactoring patches by Nickey Yang,
> > to make the Rockchip DSI driver wrap this common driver.
> > 
> > Signed-off-by: Brian Norris <briannorris@chromium.org>
> > ---
> > Could use an extra look from folks. This looks like the correct trivial
> > transformation, but I'm not that familiar with DSI.
> > 
> >   drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c | 78 ++++++---------------------
> >   1 file changed, 16 insertions(+), 62 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> > index d9cca4fd66ec..2fed20e44dfe 100644
> > --- a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> > +++ b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> > @@ -136,10 +136,6 @@
> >   					 GEN_SW_0P_TX_LP)
> >   
> >   #define DSI_GEN_HDR			0x6c
> > -/* TODO These 2 defines will be reworked thanks to mipi_dsi_create_packet() */
> > -#define GEN_HDATA(data)			(((data) & 0xffff) << 8)
> > -#define GEN_HTYPE(type)			(((type) & 0xff) << 0)
> > -
> >   #define DSI_GEN_PLD_DATA		0x70
> >   
> >   #define DSI_CMD_PKT_STATUS		0x74
> > @@ -359,44 +355,15 @@ static int dw_mipi_dsi_gen_pkt_hdr_write(struct dw_mipi_dsi *dsi, u32 hdr_val)
> >   	return 0;
> >   }
> >   
> > -static int dw_mipi_dsi_dcs_short_write(struct dw_mipi_dsi *dsi,
> > -				       const struct mipi_dsi_msg *msg)
> > -{
> > -	const u8 *tx_buf = msg->tx_buf;
> > -	u16 data = 0;
> > -	u32 val;
> > -
> > -	if (msg->tx_len > 0)
> > -		data |= tx_buf[0];
> > -	if (msg->tx_len > 1)
> > -		data |= tx_buf[1] << 8;
> > -
> > -	if (msg->tx_len > 2) {
> > -		dev_err(dsi->dev, "too long tx buf length %zu for short write\n",
> > -			msg->tx_len);
> > -		return -EINVAL;
> > -	}
> > -
> > -	val = GEN_HDATA(data) | GEN_HTYPE(msg->type);
> > -	return dw_mipi_dsi_gen_pkt_hdr_write(dsi, val);
> > -}
> > -
> > -static int dw_mipi_dsi_dcs_long_write(struct dw_mipi_dsi *dsi,
> > -				      const struct mipi_dsi_msg *msg)
> > +static int dw_mipi_dsi_dcs_write(struct dw_mipi_dsi *dsi,
> > +				 const struct mipi_dsi_packet *packet)
> 
> Both DCS and Generic dsi transfers are managed by drm_mipi_dsi.c 
> helpers. So maybe dw_mipi_dsi_dcs_write() should be renamed 
> dw_mipi_dsi_write()...

Ah, good point. I really meant to remove the _dcs naming too, but I
guess I missed it. Will follow up.

> >   {
> > -	const u8 *tx_buf = msg->tx_buf;
> > -	int len = msg->tx_len, pld_data_bytes = sizeof(u32), ret;
> > -	u32 hdr_val = GEN_HDATA(msg->tx_len) | GEN_HTYPE(msg->type);
> > +	const u8 *tx_buf = packet->payload;
> > +	int len = packet->payload_length, pld_data_bytes = sizeof(u32), ret;
> >   	u32 remainder;
> >   	u32 val;
> >   
> > -	if (msg->tx_len < 3) {
> > -		dev_err(dsi->dev, "wrong tx buf length %zu for long write\n",
> > -			msg->tx_len);
> > -		return -EINVAL;
> > -	}
> > -
> > -	while (DIV_ROUND_UP(len, pld_data_bytes)) {
> > +	while (len) {
> >   		if (len < pld_data_bytes) {
> >   			remainder = 0;
> >   			memcpy(&remainder, tx_buf, len);
> > @@ -419,40 +386,27 @@ static int dw_mipi_dsi_dcs_long_write(struct dw_mipi_dsi *dsi,
> >   		}
> >   	}
> >   
> > -	return dw_mipi_dsi_gen_pkt_hdr_write(dsi, hdr_val);
> > +	remainder = 0;
> > +	memcpy(&remainder, packet->header, sizeof(packet->header));

By the way: I don't think it's an issue that should block this patch,
since if I'm right, this function already is "broken", but isn't this
actually a bad way to handle byte-to-word marshalling? Particularly,
we're copying bytes into a word in LE ordering, but then we later write
them to IO registers with writel() (which does endian swapping).

So I think we have an endianness problem on BE systems.

One solution would be to write these to IO registers with a non-swapped
writel() (e.g., __raw_writel()? but that's not very nice...). Another
would be to avoid memcpy, and just read this out a word at a time --
that works fine for the aligned pieces, but not so well for any
non-aligned bits ('if (len < pld_data_bytes)' above) I think?

WDYT?

> > +	return dw_mipi_dsi_gen_pkt_hdr_write(dsi, remainder);
> >   }
> >   
> >   static ssize_t dw_mipi_dsi_host_transfer(struct mipi_dsi_host *host,
> >   					 const struct mipi_dsi_msg *msg)
> >   {
> >   	struct dw_mipi_dsi *dsi = host_to_dsi(host);
> > +	struct mipi_dsi_packet packet;
> >   	int ret;
> >   
> > -	/*
> > -	 * TODO dw drv improvements
> > -	 * use mipi_dsi_create_packet() instead of all following
> > -	 * functions and code (no switch cases, no
> > -	 * dw_mipi_dsi_dcs_short_write(), only the loop in long_write...)
> > -	 * and use packet.header...
> > -	 */
> > -	dw_mipi_message_config(dsi, msg);
> > -
> > -	switch (msg->type) {
> > -	case MIPI_DSI_DCS_SHORT_WRITE:
> > -	case MIPI_DSI_DCS_SHORT_WRITE_PARAM:
> > -	case MIPI_DSI_SET_MAXIMUM_RETURN_PACKET_SIZE:
> > -		ret = dw_mipi_dsi_dcs_short_write(dsi, msg);
> > -		break;
> > -	case MIPI_DSI_DCS_LONG_WRITE:
> > -		ret = dw_mipi_dsi_dcs_long_write(dsi, msg);
> > -		break;
> > -	default:
> > -		dev_err(dsi->dev, "unsupported message type 0x%02x\n",
> > -			msg->type);
> > -		ret = -EINVAL;
> > +	ret = mipi_dsi_create_packet(&packet, msg);
> > +	if (ret) {
> > +		dev_err(dsi->dev, "failed to create packet: %d\n", ret);
> > +		return ret;
> >   	}
> >   
> > -	return ret;
> > +	dw_mipi_message_config(dsi, msg);
> > +
> > +	return dw_mipi_dsi_dcs_write(dsi, &packet);
> >   }
> >   
> >   static const struct mipi_dsi_host_ops dw_mipi_dsi_host_ops = {
> > 
> 
> I performed some tests tracing all DSI_GEN_HDR & DSI_GEN_PLD_DATA reg 
> writes with panel/panel-orisetech-otm8009a.c (using long dcs commands) 
> before and after your patch and this is "100% perfect"!
> 
> So, apart the un-important "dcs" in dw_mipi_dsi_dcs_write() function name:
> 
> Reviewed-by: Philippe Cornu <philippe.cornu@st.com>
> Tested-by: Philippe Cornu <philippe.cornu@st.com>
> 
> This clean-up will help a lot to add the dsi read feature in the future.
> 
> Very good patch Brian and big "thank you" !

Thanks for the review and test! I'll likely send a v2 with only the
naming change + your tags, and I'll see about what do about the
endianness issues I noticed as a follow-up.

Brian