Re: [PATCH v2 2/2] drm/bridge/synopsys: dsi: handle endianness correctly in dw_mipi_dsi_write()

[Archit Taneja]

On 01/10/2018 08:03 PM, Andrzej Hajda wrote:
> On 09.01.2018 21:32, Brian Norris wrote:
> > We're filling the "remainder" word with little-endian data, then writing
> > it out to IO registers with endian-correcting writel(). That probably
> > won't work on big-endian systems.
> >
> > Let's mark the "remainder" variable as LE32 (since we fill it with
> > memcpy()) and do the swapping explicitly.
> >
> > Some of this function could be done more easily without memcpy(), but
> > the unaligned "remainder" case is a little hard to do without
> > potentially overrunning 'tx_buf', so I just applied the same solution in
> > all cases (memcpy() + le32_to_cpu()).
> >
> > Tested only on a little-endian system.
> >
> > Signed-off-by: Brian Norris <briannorris@xxxxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c | 18 +++++++++---------
> >   1 file changed, 9 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> > index ed91e32ee43a..90f13df6f106 100644
> > --- a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> > +++ b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> > @@ -360,18 +360,18 @@ static int dw_mipi_dsi_write(struct dw_mipi_dsi *dsi,
> >   {
> >   	const u8 *tx_buf = packet->payload;
> >   	int len = packet->payload_length, pld_data_bytes = sizeof(u32), ret;
> > -	u32 remainder;
> > +	__le32 word;
> >   	u32 val;
> >   
> >   	while (len) {
> >   		if (len < pld_data_bytes) {
> > -			remainder = 0;
> > -			memcpy(&remainder, tx_buf, len);
> > -			dsi_write(dsi, DSI_GEN_PLD_DATA, remainder);
> > +			word = 0;
> > +			memcpy(&word, tx_buf, len);
> > +			dsi_write(dsi, DSI_GEN_PLD_DATA, le32_to_cpu(word));
> >   			len = 0;
> >   		} else {
> > -			memcpy(&remainder, tx_buf, pld_data_bytes);
> > -			dsi_write(dsi, DSI_GEN_PLD_DATA, remainder);
> > +			memcpy(&word, tx_buf, pld_data_bytes);
> > +			dsi_write(dsi, DSI_GEN_PLD_DATA, le32_to_cpu(word));
> >   			tx_buf += pld_data_bytes;
> >   			len -= pld_data_bytes;
> >   		}
> > @@ -386,9 +386,9 @@ static int dw_mipi_dsi_write(struct dw_mipi_dsi *dsi,
> >   		}
> >   	}
> >   
> > -	remainder = 0;
> > -	memcpy(&remainder, packet->header, sizeof(packet->header));
> > -	return dw_mipi_dsi_gen_pkt_hdr_write(dsi, remainder);
> > +	word = 0;
> > +	memcpy(&word, packet->header, sizeof(packet->header));
> > +	return dw_mipi_dsi_gen_pkt_hdr_write(dsi, le32_to_cpu(word));
>
> You could create and use appropriate helper, lets say:
>
> u32 le_to_cpup(const u8 *p, int count)
> {
>  ÂÂÂ __le32 r = 0;
>
>  ÂÂÂ memcpy(&r, p, count);
>  ÂÂÂ return le32_to_cpu(r);
> }
>
> With or without this change:
> Reviewed-by: Andrzej Hajda <a.hajda@xxxxxxxxxxx>

Queued to drm-misc-next as is.

Thanks,
Archit

>  Â--
> Regards
> Andrzej
>
>
> >   }
> >   
> >   static ssize_t dw_mipi_dsi_host_transfer(struct mipi_dsi_host *host,

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