On Tue, 05 Sep 2023 18:06:06 +0900, 대인기/Tizen Platform Lab(SR)/삼성전자 wrote: > > > > -----Original Message----- > > From: dri-devel <dri-devel-bounces@xxxxxxxxxxxxxxxxxxxxx> On Behalf Of > > Michael Tretter > > Sent: Monday, September 4, 2023 8:15 PM > > To: Inki Dae <daeinki@xxxxxxxxx> > > Cc: Neil Armstrong <neil.armstrong@xxxxxxxxxx>; Robert Foss > > <rfoss@xxxxxxxxxx>; Jonas Karlman <jonas@xxxxxxxxx>; dri- > > devel@xxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Jernej Skrabec > > <jernej.skrabec@xxxxxxxxx>; Laurent Pinchart > > <Laurent.pinchart@xxxxxxxxxxxxxxxx>; Andrzej Hajda > > <andrzej.hajda@xxxxxxxxx>; Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>; > > kernel@xxxxxxxxxxxxxx; Jagan Teki <jagan@xxxxxxxxxxxxxxxxxxxx> > > Subject: Re: [PATCH 3/5] drm/bridge: samsung-dsim: update PLL reference > > clock > > > > On Mon, 04 Sep 2023 14:44:41 +0900, Inki Dae wrote: > > > 2023년 8월 29일 (화) 오전 12:59, Michael Tretter <m.tretter@xxxxxxxxxxxxxx> > > 님이 작성: > > > > > > > > The PLL requires a clock between 2 MHz and 30 MHz after the pre- > > divider. > > > > The reference clock for the PLL may change due to changes to it's > > parent > > > > clock. Thus, the frequency may be out of range or unsuited for > > > > generating the high speed clock for MIPI DSI. > > > > > > > > Try to keep the pre-devider small, and set the reference clock close > > to > > > > 30 MHz before recalculating the PLL configuration. Use a divider with > > a > > > > power of two for the reference clock as this seems to work best in > > > > my tests. > > > > > > Clock frequency is specific to SoC architecture so we have to handle > > > it carefully because samsung-dsim.c is a common module for I.MX and > > > Exynos series. > > > You mentioned "The PLL requires a clock between 2 MHz and 3MHz after > > > pre-divider", and the clock means that fin_pll - PFD input frequency - > > > which can be calculated with oscillator clock frequency / P value? > > > According to Exynos datasheet, the fin_pll should be 6 ~ 12Mhz. > > > > > > For example, > > > In case of Exyhos, we use 24MHz as oscillator clock frequency, so > > > fin_pll frequency, 8MHz = 24MHz / P(3). > > > > > > Can you tell me the source of the constraint that clocks must be > > > between 2MHz and 30MHz? > > > > The source is the i.MX8M Nano reference manual, Table 13-40. DPHY PLL > > Parameters. It documents that the P divider frequency (fin_pll) has a > > frequency range of 2 MHz to 30 MHz. According to the same table, the input Small clarification: These are the corrected limits of TRM rev. 1. In TRM rev. 0 the limits are incorrectly specified as 6 MHz to 12 MHz. > > In case of Exynos, the range is from 6MHz to 12MHz according to Exynos4212 reference manual, Table 1-5. > > > frequency (fin) has a range of 6 MHz to 300 MHz. > > In case of Exynos, the range is from 6MHz to 200MHz. > > > > > Is the table incorrect? > > It's correct for I.MX but incorrect for Exynos. I think it would mean that > the valid range depends on SoC architecture. So I'd say that this patch is > specific to I.MX. I understand. > This was one of what I concerted about when trying to move > samsung-dsim.c module to bridge directory for common use between I.MX and > Exynos Platforms, and this will be what we have to solve together - I.MX and > Exynos engineers. How about using platform specific data - > samsung_dsim_driver_data structure? > > I.e, > > static const struct samsung_dsim_driver_data imx8mm_dsi_driver_data = { > ... > .min_fin_pll = 2, > .max_fin_pll = 30, > ... > }; > > static const struct samsung_dsim_driver_data exynosxxxx_dsi_driver_data = { > ... > .min_fin_pll = 6, > .max_fin_pll = 12, > ... > }; Extending the samsung_dsim_driver_data sounds reasonable. There are already other frequency limits specified. I will implement this in v2. > > And then, > > while (fin > driver_data->max_fin_pll * MHZ) > fin = fin / 2; > > > > > I also tried to always set the reference clock to 24 MHz, but depending on > > the > > display clock this isn't always possible. > > According to dt binding, if samsung,pll-clock-frequency exists then we have > to use it first. I'm not sure but could we check if the pll_clk_rate is > valid or not depending on the given display clock in advance? If so then > maybe we could update the pll_clk_rate correctly by reading the pll_clk > frequency again. If samsung,pll-clock-frequency is set, the driver will neither check nor update the pll_clk, but assume that the clocks are configured correctly. Thus, the author of the device tree is responsible for selecting and configuring valid clocks. I observed that if I set pll_clk to any fixed value for different modes, the clock framework may use a different clock rate depending on what is possible. This may result in a reference clock that uses a fractional divider to get the pll_clk_rate or cannot exactly produce the hs_clock. These situations cause sync issues on the display. Checking, if the current pll_clk_rate would involve the pix_clk, the hs_clock, and the parent of the pll_clk. It may be possible, but I don't see a problem with calculating a suitable pll_clk_rate, updating the pll_clk, and then configuring the PLL to generate the hs_clock. Michael > > Thanks, > Inki Dae > > > > > Michael > > > > > > > > To other I.MX and Exynos engineers, please do not merge this patch > > > until two SoC platforms are tested correctly. > > > > > > Thanks, > > > Inki Dae > > > > > > > > > > > Signed-off-by: Michael Tretter <m.tretter@xxxxxxxxxxxxxx> > > > > --- > > > > drivers/gpu/drm/bridge/samsung-dsim.c | 15 +++++++++++++-- > > > > 1 file changed, 13 insertions(+), 2 deletions(-) > > > > > > > > diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c > > b/drivers/gpu/drm/bridge/samsung-dsim.c > > > > index da90c2038042..4de6e4f116db 100644 > > > > --- a/drivers/gpu/drm/bridge/samsung-dsim.c > > > > +++ b/drivers/gpu/drm/bridge/samsung-dsim.c > > > > @@ -611,10 +611,21 @@ static unsigned long samsung_dsim_set_pll(struct > > samsung_dsim *dsi, > > > > u16 m; > > > > u32 reg; > > > > > > > > - if (dsi->pll_clk) > > > > + if (dsi->pll_clk) { > > > > + /* > > > > + * Ensure that the reference clock is generated with a > > power of > > > > + * two divider from its parent, but close to the PLLs > > upper > > > > + * limit of the valid range of 2 MHz to 30 MHz. > > > > + */ > > > > + fin = clk_get_rate(clk_get_parent(dsi->pll_clk)); > > > > + while (fin > 30 * MHZ) > > > > + fin = fin / 2; > > > > + clk_set_rate(dsi->pll_clk, fin); > > > > + > > > > fin = clk_get_rate(dsi->pll_clk); > > > > - else > > > > + } else { > > > > fin = dsi->pll_clk_rate; > > > > + } > > > > dev_dbg(dsi->dev, "PLL ref clock freq %lu\n", fin); > > > > > > > > fout = samsung_dsim_pll_find_pms(dsi, fin, freq, &p, &m, &s); > > > > > > > > -- > > > > 2.39.2 > > > > > > > > > >