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SubjectRe: [PATCH v2] drm/bridge/synopsys: dsi: add optional pixel clock
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Hi Andrzej,

On 01/15/2018 02:52 PM, Andrzej Hajda wrote:
> On 12.01.2018 17:25, Philippe Cornu wrote:
>> The pixel clock is optional. When available, it offers a better
>> preciseness for timing computations and allows to reduce the extra dsi
>> bandwidth in burst mode (from ~20% to ~10-12%, hw platform dependent).
>>
>> Signed-off-by: Philippe Cornu <philippe.cornu@st.com>
>> ---
>> Changes in v2: Improve px_clk probing in case of ENOENT dt returned value
>> (thanks to Philipp Zabel & Andrzej Hajda comments)
>>
>> drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c | 26 ++++++++++++++++++++------
>> 1 file changed, 20 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
>> index c39c7dce20ed..62fcff881b98 100644
>> --- a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
>> +++ b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
>> @@ -225,6 +225,7 @@ struct dw_mipi_dsi {
>> void __iomem *base;
>>
>> struct clk *pclk;
>> + struct clk *px_clk;
>>
>> unsigned int lane_mbps; /* per lane */
>> u32 channel;
>> @@ -753,24 +754,28 @@ void dw_mipi_dsi_bridge_mode_set(struct drm_bridge *bridge,
>> struct dw_mipi_dsi *dsi = bridge_to_dsi(bridge);
>> const struct dw_mipi_dsi_phy_ops *phy_ops = dsi->plat_data->phy_ops;
>> void *priv_data = dsi->plat_data->priv_data;
>> + struct drm_display_mode px_clk_mode = *mode;
>> int ret;
>>
>> clk_prepare_enable(dsi->pclk);
>>
>> - ret = phy_ops->get_lane_mbps(priv_data, mode, dsi->mode_flags,
>> + if (dsi->px_clk)
>> + px_clk_mode.clock = clk_get_rate(dsi->px_clk) / 1000;
>> +
>> + ret = phy_ops->get_lane_mbps(priv_data, &px_clk_mode, dsi->mode_flags,
>> dsi->lanes, dsi->format, &dsi->lane_mbps);
>> if (ret)
>> DRM_DEBUG_DRIVER("Phy get_lane_mbps() failed\n");
>>
>> pm_runtime_get_sync(dsi->dev);
>> dw_mipi_dsi_init(dsi);
>> - dw_mipi_dsi_dpi_config(dsi, mode);
>> + dw_mipi_dsi_dpi_config(dsi, &px_clk_mode);
>> dw_mipi_dsi_packet_handler_config(dsi);
>> dw_mipi_dsi_video_mode_config(dsi);
>> - dw_mipi_dsi_video_packet_config(dsi, mode);
>> + dw_mipi_dsi_video_packet_config(dsi, &px_clk_mode);
>> dw_mipi_dsi_command_mode_config(dsi);
>> - dw_mipi_dsi_line_timer_config(dsi, mode);
>> - dw_mipi_dsi_vertical_timing_config(dsi, mode);
>> + dw_mipi_dsi_line_timer_config(dsi, &px_clk_mode);
>> + dw_mipi_dsi_vertical_timing_config(dsi, &px_clk_mode);
>>
>> dw_mipi_dsi_dphy_init(dsi);
>> dw_mipi_dsi_dphy_timing_config(dsi);
>> @@ -784,7 +789,7 @@ void dw_mipi_dsi_bridge_mode_set(struct drm_bridge *bridge,
>>
>> dw_mipi_dsi_dphy_enable(dsi);
>>
>> - dw_mipi_dsi_wait_for_two_frames(mode);
>> + dw_mipi_dsi_wait_for_two_frames(&px_clk_mode);
>>
>> /* Switch to cmd mode for panel-bridge pre_enable & panel prepare */
>> dw_mipi_dsi_set_mode(dsi, 0);
>> @@ -878,6 +883,15 @@ __dw_mipi_dsi_probe(struct platform_device *pdev,
>> return ERR_PTR(ret);
>> }
>>
>> + dsi->px_clk = devm_clk_get(dev, "px_clk");
>> + if (PTR_ERR(dsi->px_clk) == -ENOENT) {
>> + dsi->px_clk = NULL;
>> + } else if (IS_ERR(dsi->px_clk)) {
>> + ret = PTR_ERR(dsi->px_clk);
>> + dev_err(dev, "Unable to get optional px_clk: %d\n", ret);
>> + dsi->px_clk = NULL;
>> + }
>> +
> As I understand on fail you just log an error and continue?
> The code could be slightly simplified, for example:
> dsi->px_clk = devm_clk_get(dev, "px_clk");
> if (IS_ERR(dsi->px_clk)) {
>         ret = PTR_ERR(dsi->px_clk);
>         if (ret != ENOENT)
>                 dev_err(dev, "Unable to get optional px_clk: %d\n", ret);
>         dsi->px_clk = NULL;
> }
>
> With or without this change:
>
> Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
>

Thanks for your review.

Yes in this version, on fail, I just log an error and continue,
especially because this px_clk is "optional" in the documentation. Then
your proposal is much better than mine : )

Nevertheless, I wonder now if it could be better to "return" in case of
error as we do for others mandatory clocks...
So then, the code could be:

dsi->px_clk = devm_clk_get(dev, "px_clk");
if (IS_ERR(dsi->px_clk)) {
dsi->px_clk = NULL;
ret = PTR_ERR(dsi->px_clk);
if (ret != ENOENT) {
dev_err(dev, "Unable to get optional px_clk: %d\n", ret);
return ERR_PTR(ret);
}
}


Do you (or someone else) have a preferred choice?


Many thanks,
Philippe :-)

>  --
> Regards
> Andrzej
>
>
>> /*
>> * Note that the reset was not defined in the initial device tree, so
>> * we have to be prepared for it not being found.
>
>
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