linux-kernel - Re: [Intel-gfx] [PATCH 2/2] drm/i915/edp/jsl: Update vswing table for HBR and HBR2

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Date:   Mon, 28 Sep 2020 16:07:39 -0700
From:   Lucas De Marchi <lucas.demarchi@...el.com>
To:     Jani Nikula <jani.nikula@...ux.intel.com>
Cc:     "Surendrakumar Upadhyay, TejaskumarX" 
        <tejaskumarx.surendrakumar.upadhyay@...el.com>,
        "Vivi, Rodrigo" <rodrigo.vivi@...el.com>,
        "airlied@...ux.ie" <airlied@...ux.ie>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Ausmus, James" <james.ausmus@...el.com>,
        "Roper, Matthew D" <matthew.d.roper@...el.com>,
        "Souza, Jose" <jose.souza@...el.com>,
        "ville.syrjala@...ux.intel.com" <ville.syrjala@...ux.intel.com>,
        "Pandey, Hariom" <hariom.pandey@...el.com>
Subject: Re: [Intel-gfx] [PATCH 2/2] drm/i915/edp/jsl: Update vswing table
 for HBR and HBR2

On Mon, Sep 28, 2020 at 08:15:29PM +0300, Jani Nikula wrote:
>On Mon, 28 Sep 2020, "Surendrakumar Upadhyay, TejaskumarX"	<tejaskumarx.surendrakumar.upadhyay@...el.com> wrote:
>> This is a good example of a potential trap that having
>> IS_ELKHARTLAKE() cover both ELK and JSP creates. An unsuspecting coder
>> might change the if ladder to have IS_ELKHARTLAKE() first, and the
>> subsequent IS_JASPERLAKE() branch would never be taken.
>>
>> BR,
>> Jani.
>>
>> Tejas : In that case I will put attention note in comment about
>> platform checks such that ladder distrubance can be avoided. What you
>> suggest?

>The solution is to make IS_ELKHARTLAKE() mean ELK and only ELK.

Since we are talking about the TLA for JSL in the other patch, for
elkhartlake it is EHL, not ELK. ELK is something else, but I'm not sure
what:

$ git grep -w ELK -- drivers/gpu/drm/
drivers/gpu/drm/i915/gem/i915_gem_stolen.c:             IS_GM45(i915) ? "CTG" : "ELK", reg_val);
drivers/gpu/drm/i915/gem/i915_gem_stolen.c:      * Whether ILK really reuses the ELK register for this is unclear.
drivers/gpu/drm/i915/intel_pm.c:         * Not 100% sure which way ELK should go here as the
drivers/gpu/drm/i915/intel_pm.c:         * assume ELK doesn't need this.

Lucas De Marchi

>
>BR,
>Jani.
>
>
>-- 
>Jani Nikula, Intel Open Source Graphics Center