linux-kernel - Re: [PATCH 1/3] drm/dsi: Add support for Turn on/Shutdown peripheral packets

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Date:	Tue, 24 Nov 2015 08:02:20 -0800
From:	Bjorn Andersson <bjorn@...o.se>
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	David Airlie <airlied@...ux.ie>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH 1/3] drm/dsi: Add support for Turn on/Shutdown peripheral packets

On Tue, Nov 24, 2015 at 1:33 AM, Thierry Reding
<thierry.reding@...il.com> wrote:
> On Fri, Oct 30, 2015 at 05:38:26PM -0700, bjorn@...o.se wrote:
>> From: Werner Johansson <werner.johansson@...ymobile.com>
>>
>> The MIPI_DSI_TURN_ON_PERIPHERAL and MIPI_DSI_SHUTDOWN_PERIPHERAL
>> packets are required for some panels, one example being the
>> Panasonic VVX10F034N00 panel.
>>
>> Signed-off-by: Werner Johansson <werner.johansson@...ymobile.com>
>> Signed-off-by: Bjorn Andersson <bjorn.andersson@...ymobile.com>
>> ---
>>  drivers/gpu/drm/drm_mipi_dsi.c | 47 ++++++++++++++++++++++++++++++++++++++++++
>>  include/drm/drm_mipi_dsi.h     |  3 +++
>>  2 files changed, 50 insertions(+)
>
> This being a dependency on 3/3 it would've been good to send this To: me
> as well. I hadn't seen this in my inbox and had simply discarded it as
> being independent. Of course if I had properly checked the build I
> would've noticed...
>

Sorry for not including you as a recipient, I relied too heavily on
get_maintainer. Thanks for fixing my misstake.

> Anyway, I've applied this with slight modifications. I removed the raw
> short write helper. I don't think it buys us much and we already have an
> open-coded variant in mipi_dsi_set_maximum_return_packet_size(). I've
> also moved these functions closer to the Set Maximum Return Packet Size
> command implementation because they are part of the same command set. I
> also made the functions return int instead of ssize_t to avoid potential
> confusion about their return value (ssize_t implies "number of bytes
> transferred, or a negative error code on failure).
>

Sounds good, thanks.

> One minor comment below...
>
>> diff --git a/drivers/gpu/drm/drm_mipi_dsi.c b/drivers/gpu/drm/drm_mipi_dsi.c
>> index 2d5ca8ee..13b4a9c 100644
>> --- a/drivers/gpu/drm/drm_mipi_dsi.c
>> +++ b/drivers/gpu/drm/drm_mipi_dsi.c
>> @@ -862,6 +862,53 @@ int mipi_dsi_dcs_set_pixel_format(struct mipi_dsi_device *dsi, u8 format)
>>  }
>>  EXPORT_SYMBOL(mipi_dsi_dcs_set_pixel_format);
>>
>> +/**
>> + * mipi_dsi_raw_short_write() - Sends a data-less short DSI packet
>> + * @dsi: DSI peripheral device
>> + * @type: Data Type of packet to send
>> + *
>> + * Return: 0 on success or a negative error code on failure.
>> + */
>> +static ssize_t mipi_dsi_raw_short_write(struct mipi_dsi_device *dsi, u8 type)
>> +{
>> +     u8 dummy[2] = { 0, 0 };
>> +     struct mipi_dsi_msg msg = {
>> +             .channel = dsi->channel,
>> +             .tx_buf = dummy,
>> +             .tx_len = sizeof(dummy),
>> +             .type = type
>> +     };
>> +
>> +     if (mipi_dsi_packet_format_is_short(type))
>> +             return mipi_dsi_device_transfer(dsi, &msg);
>> +     else
>> +             return -1;
>> +}
>
> When the kerneldoc comment says "negative error code", developers will
> expect one of the -E* constants. -1 maps to -EPERM (operation not
> permitted), which isn't a good error code for this case. This is also an
> internal function, so these errors really should never happen.
>
> Anyway, since I removed this helper this isn't an issue anymore, just
> wanted to mention it.
>

Right. Thanks for fixing it!

Regards,
Bjorn
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