Re: [PATCH] drm/i915/gmbus: Add Wa_16025573575 for PTL for bit-bashing

[Gustavo Sousa <gustavo.sousa@intel.com>]

Quoting Ankit Nautiyal (2025-06-12 04:53:30-03:00)
>As per Wa_16025573575 for PTL, set the GPIO masks bit before starting
>bit-bashing and maintain value through the bit-bashing sequence.
>After bit-bashing sequence is done, clear the GPIO masks bits.
>
>Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
>---
> drivers/gpu/drm/i915/display/intel_gmbus.c | 38 +++++++++++++++++++---
> 1 file changed, 34 insertions(+), 4 deletions(-)
>
>diff --git a/drivers/gpu/drm/i915/display/intel_gmbus.c b/drivers/gpu/drm/i915/display/intel_gmbus.c
>index 0d73f32fe7f1..c96167c70228 100644
>--- a/drivers/gpu/drm/i915/display/intel_gmbus.c
>+++ b/drivers/gpu/drm/i915/display/intel_gmbus.c
>@@ -242,10 +242,17 @@ static u32 get_reserved(struct intel_gmbus *bus)
>         struct intel_display *display = bus->display;
>         u32 reserved = 0;
> 
>-        /* On most chips, these bits must be preserved in software. */
>-        if (!display->platform.i830 && !display->platform.i845g)
>-                reserved = intel_de_read_notrace(display, bus->gpio_reg) &
>-                        (GPIO_DATA_PULLUP_DISABLE | GPIO_CLOCK_PULLUP_DISABLE);
>+        if (!display->platform.i830 && !display->platform.i845g) {

I believe the stuff specific to Wa_16025573575 could be done in a
separate "if" statement. The conditions for Wa_16025573575 already imply
(!display->platform.i830 && !display->platform.i845g), and using in a
separate "if" statement reduces one indentation level :-)

That would mean moving preserve_bits one level up, making it available
in the function's scope and doing the registers read conditioned on
preserve_bits being non-zero.

>+                /* On most chips, these bits must be preserved in software. */
>+                u32 preserve_bits = GPIO_DATA_PULLUP_DISABLE | GPIO_CLOCK_PULLUP_DISABLE;
>+
>+                /* PTL: Wa_16025573575: the masks bits need to be preserved through out */
>+                if (DISPLAY_VER(display) == 30)

Instead of open-coding the conditions for the workaround in three
different places in the file, I think we should have a function
needs_wa_16025573575() and use it.

Also, note that the workaround is also required for WCL (display version
30.02), and we would then include that in needs_wa_16025573575().

--
Gustavo Sousa

>+                        preserve_bits |= GPIO_CLOCK_DIR_MASK | GPIO_CLOCK_VAL_MASK |
>+                                         GPIO_DATA_DIR_MASK | GPIO_DATA_VAL_MASK;
>+
>+                reserved = intel_de_read_notrace(display, bus->gpio_reg) & preserve_bits;
>+        }
> 
>         return reserved;
> }
>@@ -308,6 +315,23 @@ static void set_data(void *data, int state_high)
>         intel_de_posting_read(display, bus->gpio_reg);
> }
> 
>+/* PTL: Wa_16025573575 */
>+static void
>+ptl_handle_mask_bits(struct intel_gmbus *bus, bool set)
>+{
>+        struct intel_display *display = bus->display;
>+        u32 reg_val = intel_de_read_notrace(display, bus->gpio_reg);
>+        u32 mask_bits = GPIO_CLOCK_DIR_MASK | GPIO_CLOCK_VAL_MASK |
>+                        GPIO_DATA_DIR_MASK | GPIO_DATA_VAL_MASK;
>+        if (set)
>+                reg_val |= mask_bits;
>+        else
>+                reg_val &= ~mask_bits;
>+
>+        intel_de_write_notrace(display, bus->gpio_reg, reg_val);
>+        intel_de_posting_read(display, bus->gpio_reg);
>+}
>+
> static int
> intel_gpio_pre_xfer(struct i2c_adapter *adapter)
> {
>@@ -319,6 +343,9 @@ intel_gpio_pre_xfer(struct i2c_adapter *adapter)
>         if (display->platform.pineview)
>                 pnv_gmbus_clock_gating(display, false);
> 
>+        if (DISPLAY_VER(display) == 30)
>+                ptl_handle_mask_bits(bus, true);
>+
>         set_data(bus, 1);
>         set_clock(bus, 1);
>         udelay(I2C_RISEFALL_TIME);
>@@ -336,6 +363,9 @@ intel_gpio_post_xfer(struct i2c_adapter *adapter)
> 
>         if (display->platform.pineview)
>                 pnv_gmbus_clock_gating(display, true);
>+
>+        if (DISPLAY_VER(display) == 30)
>+                ptl_handle_mask_bits(bus, false);
> }
> 
> static void
>-- 
>2.45.2
>