On 5/15/2023 3:01 PM, Marijn Suijten wrote:
On 2023-05-15 13:29:21, Jessica Zhang wrote:
<snip>
Const, as requested elsewhere. But this function is not used anywhere
in any of the series (because we replaced the usages with more sensible
member accesses like slice_chunk_size).
Acked.
I would prefer to keep this helper so that we have a way to easily get
BPP information from the DRM DSC config in the future, but if you'd
prefer we add this helper then, I'm also ok with that.
The inverse helper is available ad DSC_BPP in drm_dsc_helper.c. Perhaps
we can move the two variants to the header and define them uniformly?
This isn't MSM-specific it seems (i.e. the format supports fractional
bpp but no RC parameters appear to be defined for such a format yet).
<snip>
+ * @dsc: Pointer to drm dsc config struct
+ * Returns: Integer value representing pclk per interface
+ *
+ * Note: This value will then be passed along to DSI and DP for some more
+ * calculations. This is because DSI and DP divide the pclk_per_intf value
+ * by different values depending on if widebus is enabled.
Can you elaborate what this "note" is trying to tell users of this
function? That they should not use bytes_per_line raw? That it doesn't
actually represent bytes_per_line if the extra calculations mentioned
here are not applied?
The latter -- this method is used for calculating the pclk for DSI and
DP. While it does get the raw bytes_per_line, there are some extra
calculations needed before it can be set as the pclk_rate. These "extra
calculations" are different between DP and DSI.
For more context, please refer to the earlier revisions of this patch
and the usage of the helper in dsi_host.c
Note that I'm not just asking to explain it to me, but to explain it in
the documentation. The function is named bytes_per_line() but then
Returns: says it returns the pclk per interface, then the note says that
it actually doesn't unless extra calculations are applied.
We can explain the same much more concisely by rewriting Returns and
dropping Note:
Returns: Integer value representing bytes per line. DSI and DP need
to perform further processing/calculations to turn this into
pclk_per_intf, such as dividing by different values depending on
if widebus is enabled.
And so we have written the same, just more concisely. Feel free to
reword it slightly, such as dropping the word "processing".
Sure, sounds good.
<snip>
Not sure that this helper is useful though: it is
only used where msm_dsc_get_slice_per_intf() was already called, so it
makes more sense to the reader to just multiply slice_per_intf by
slice_chunk_size than to defer to an opaque helper.
I would prefer to keep this as a helper as this math is common between
DP and DSI, and I believe the name of the helper accurately reflects
what is being calculated.
If there's any confusion with the name of the method, I am open to
suggestions.
The name is good, I'm just not too keen on it hiding the multiplication
with msm_dsc_get_slice_per_intf() which is already also computed and
available in DSI, and I assume DP too?
Got it, I see why you want to make that change now. DP only uses
get_slice_per_intf() to get eol_byte_num similarly to DSI, so I can just
do that then.
Thanks,
Jessica Zhang
- Marijn
