Messages in this thread | | | Date | Mon, 31 Jul 2023 11:32:32 +0300 | Subject | Re: [PATCH v7 2/4] drm/mediatek: Fix using wrong drm private data to bind mediatek-drm | From | Eugen Hristev <> |
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On 7/31/23 11:21, Jason-JH Lin (林睿祥) wrote: > Hi Eugen, > > Thanks for the reviews. > > On Fri, 2023-07-28 at 11:47 +0300, Eugen Hristev wrote: >> Hi, >> >> On 7/27/23 19:41, Jason-JH.Lin wrote: >>> Add checking the length of each data path before assigning drm >>> private >>> data into all_drm_priv array. >>> >>> Fixes: 1ef7ed48356c ("drm/mediatek: Modify mediatek-drm for mt8195 >>> multi mmsys support") >>> Signed-off-by: Jason-JH.Lin <jason-jh.lin@mediatek.com> >>> --- >>> drivers/gpu/drm/mediatek/mtk_drm_drv.c | 16 +++++++++++++--- >>> 1 file changed, 13 insertions(+), 3 deletions(-) >>> >>> diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.c >>> b/drivers/gpu/drm/mediatek/mtk_drm_drv.c >>> index 249c9fd6347e..d2fb1fb4e682 100644 >>> --- a/drivers/gpu/drm/mediatek/mtk_drm_drv.c >>> +++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.c >>> @@ -351,6 +351,7 @@ static bool mtk_drm_get_all_drm_priv(struct >>> device *dev) >>> { >>> struct mtk_drm_private *drm_priv = dev_get_drvdata(dev); >>> struct mtk_drm_private *all_drm_priv[MAX_CRTC]; >>> + struct mtk_drm_private *temp_drm_priv; >>> struct device_node *phandle = dev->parent->of_node; >>> const struct of_device_id *of_id; >>> struct device_node *node; >>> @@ -373,9 +374,18 @@ static bool mtk_drm_get_all_drm_priv(struct >>> device *dev) >>> if (!drm_dev || !dev_get_drvdata(drm_dev)) >>> continue; >>> >>> - all_drm_priv[cnt] = dev_get_drvdata(drm_dev); >>> - if (all_drm_priv[cnt] && all_drm_priv[cnt]- >>>> mtk_drm_bound) >>> - cnt++; >>> + temp_drm_priv = dev_get_drvdata(drm_dev); >>> + if (temp_drm_priv) { >>> + if (temp_drm_priv->mtk_drm_bound) >>> + cnt++; >>> + >>> + if (temp_drm_priv->data->main_len) >>> + all_drm_priv[0] = temp_drm_priv; >>> + else if (temp_drm_priv->data->ext_len) >>> + all_drm_priv[1] = temp_drm_priv; >>> + else if (temp_drm_priv->data->third_len) >>> + all_drm_priv[2] = temp_drm_priv; >>> + } >> >> Previously the code was assigning stuff into all_drm_priv[cnt] and >> incrementing it. >> With your change, it assigns to all_drm_priv[0], [1], [2]. Is this >> what >> you intended ? > > Because dev_get_drvdata(drm_dev) will get the driver data by drm_dev. > Each drm_dev represents a display path. > e,g. > drm_dev of "mediatek,mt8195-vdosys0" represents main path. > drm_dev of "mediatek,mt8195-vdosys1" represents ext path. > > So we want to make sure all_drm_priv[] store the private data in > the order of display path, such as: > all_drm_priv[0] = the private data of main display > all_drm_priv[1] = the private data of ext display > all_drm_priv[2] = the private data of third display
If you have such a hard requirement for keeping elements in an array, you are better having drm_priv_main_display drm_priv_ext_display drm_priv_third_display
Keeping them indexed in a three elements array by having no logical connection between the number [0,1,2] and the actual displays that you want to save is a bit confusing.
One other option which I don't know if it's better or not is to have macros to hide your indexed approach: all_drm_priv[MAIN_DISPLAY] ... etc.
> >> If this loop has second run, you will reassign to all_drm_priv again >> ? > > Because the previous code will store all_drm_priv[] in the order of > mtk_drm_bind() was called. > > If drm_dev of ext path bound earlier than drm_dev of main path, > all_drm_priv[] in mtk_drm_get_all_drm_priv() may be re-assigned like > this: > all_drm_priv[0]->all_drm_priv[0] = private data of ext path > all_drm_priv[1]->all_drm_priv[0] = private data of ext path > all_drm_priv[0]->all_drm_priv[1] = private data of main path > all_drm_priv[1]->all_drm_priv[1] = private data of main path > > But we expect all_drm_priv[] be re-assigned like this: > all_drm_priv[0]->all_drm_priv[0] = private data of main path > all_drm_priv[1]->all_drm_priv[0] = private data of main path > all_drm_priv[0]->all_drm_priv[1] = private data of ext path > all_drm_priv[1]->all_drm_priv[1] = private data of ext path
This expectation does not appear to be really enforced in your code. You have a driver that keeps an array with all_drm_priv[], in which you can have main path or ext path. Then it's natural that they might have whichever order in the array you are placing them into. If you have a hard enforced order of keeping elements in your array, then an indexed array is not the best option here. You can either: move to a different type of array , with macros for indexes into the array, or, store a second array/field which keeps the index in which you saved each element.
This is just my opinion , by looking at your code.
> >> I would expect you to take `cnt` into account. >> Also, is it expected that all_drm_priv has holes in the array ? > > Each drm_dev will only called mtk_drm_bind() once, so all holes > will be filled after all drm_dev has called mtk_drm_bind(). > > Do you agree with this statement? :)
At the moment I cannot agree nor disagree, I don't know the code well enough. But what I can say, is that you should not rely on future calls of the function to fill up your array correctly.
> > Regards, > Jason-JH.Lin > >> >> Eugen >> >> >> >>> } >>> >>> if (drm_priv->data->mmsys_dev_num == cnt) { >> >>
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