On Tue, Nov 04, 2014 at 03:21:14PM +0100, Andrzej Hajda wrote:
> On 11/04/2014 02:58 PM, Thierry Reding wrote:
> > On Tue, Nov 04, 2014 at 12:43:21PM +0100, Andrzej Hajda wrote:
> >> On 11/03/2014 10:13 AM, Thierry Reding wrote:
[...]
> >>> diff --git a/drivers/gpu/drm/drm_mipi_dsi.c b/drivers/gpu/drm/drm_mipi_dsi.c
[...]
> >>> + packet->header[1] = (msg->tx_len >> 0) & 0xff;
> >>> + packet->header[2] = (msg->tx_len >> 8) & 0xff;
> >>> +
> >>> + packet->payload_length = msg->tx_len;
> >>> + packet->payload = tx;
> >>> + } else {
> >>> + packet->header[1] = (msg->tx_len > 0) ? tx[0] : 0;
> >>> + packet->header[2] = (msg->tx_len > 1) ? tx[1] : 0;
> >>> + }
> >>> +
> >>> + packet->size = sizeof(packet->header) + packet->payload_length;
> >> size seems to be completely useless.
> > It's not. Tegra has two FIFOs that can be selected depending on the size
> > of a transfer. I use this field to detect which FIFO needs to be
> > selected.
>
> But size is always equal payload_length + 4, so it does not carry any
> additional information.
Right, but it's out of convenience to prevent every driver from doing
this again. It's part of the help that the helper provides. =)
> >>> +
> >>> + return 0;
> >>> +}
> >>> +EXPORT_SYMBOL(mipi_dsi_create_packet);
> >>> +
> >>> +/**
> >>> * mipi_dsi_dcs_write - send DCS write command
> >>> * @dsi: DSI device
> >>> * @data: pointer to the command followed by parameters
> >>> diff --git a/include/drm/drm_mipi_dsi.h b/include/drm/drm_mipi_dsi.h
> >>> index 8569dc5a1026..663aa68826f4 100644
> >>> --- a/include/drm/drm_mipi_dsi.h
> >>> +++ b/include/drm/drm_mipi_dsi.h
> >>> @@ -44,6 +44,24 @@ struct mipi_dsi_msg {
> >>> };
> >>>
> >>> /**
> >>> + * struct mipi_dsi_packet - represents a MIPI DSI packet in protocol format
> >>> + * @size: size (in bytes) of the packet
> >>> + * @header: the four bytes that make up the header (Data ID, Word Count or
> >>> + * Packet Data, and ECC)
> >>> + * @payload_length: number of bytes in the payload
> >>> + * @payload: a pointer to a buffer containing the payload, if any
> >>> + */
> >>> +struct mipi_dsi_packet {
> >>> + size_t size;
> >>> + u8 header[4];
> >> I wonder if it wouldn't be good to make it u32 or at least anonymous union:
> >> union {
> >> u8 header[4];
> >> u32 header32;
> >> };
> > I'm not sure this is very useful. It's pretty trivial how you
> > concatenate the individual bytes and it actually remove any ambiguity
> > about the endianness.
>
> This looks better:
>
> val = le16_to_cpu(pkt->header32);
> writel(val, REG);
>
> than this:
>
> val = pkt->header[2] << 16 | pkt->header[1] << 8 | pkt->header[0];
> writel(val, REG);
I disagree. =) Having the individual bytes makes their ordering very
explicit.
Thierry
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