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[80.7.220.175]) by smtp.gmail.com with ESMTPSA id l18-20020a05600c1d1200b003a04d19dab3sm29367538wms.3.2022.07.25.03.31.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 25 Jul 2022 03:31:30 -0700 (PDT) Date: Mon, 25 Jul 2022 11:31:28 +0100 From: Daniel Thompson To: ChiaEn Wu Cc: lee.jones@linaro.org, jingoohan1@gmail.com, pavel@ucw.cz, robh+dt@kernel.org, krzysztof.kozlowski+dt@linaro.org, matthias.bgg@gmail.com, sre@kernel.org, chunfeng.yun@mediatek.com, gregkh@linuxfoundation.org, jic23@kernel.org, lars@metafoo.de, lgirdwood@gmail.com, broonie@kernel.org, linux@roeck-us.net, heikki.krogerus@linux.intel.com, deller@gmx.de, andy.shevchenko@gmail.com, chiaen_wu@richtek.com, alice_chen@richtek.com, cy_huang@richtek.com, dri-devel@lists.freedesktop.org, linux-leds@vger.kernel.org, devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, linux-usb@vger.kernel.org, linux-iio@vger.kernel.org, linux-fbdev@vger.kernel.org, szunichen@gmail.com Subject: Re: [PATCH v6 13/13] video: backlight: mt6370: Add MediaTek MT6370 support Message-ID: <20220725103128.xtaw2c4y5fobowg7@maple.lan> References: <20220722102407.2205-1-peterwu.pub@gmail.com> <20220722102407.2205-14-peterwu.pub@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220722102407.2205-14-peterwu.pub@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 22, 2022 at 06:24:07PM +0800, ChiaEn Wu wrote: > diff --git a/drivers/video/backlight/Kconfig b/drivers/video/backlight/Kconfig > index a003e02..846dbe7 100644 > --- a/drivers/video/backlight/Kconfig > +++ b/drivers/video/backlight/Kconfig > @@ -268,6 +268,18 @@ config BACKLIGHT_MAX8925 > If you have a LCD backlight connected to the WLED output of MAX8925 > WLED output, say Y here to enable this driver. > > +config BACKLIGHT_MT6370 > + tristate "MediaTek MT6370 Backlight Driver" > + depends on MFD_MT6370 > + help > + This enables support for Mediatek MT6370 Backlight driver. > + It's commonly used to drive the display WLED. There are 4 channels > + inside, and each channel supports up to 30mA of current capability > + with 2048 current steps in exponential or linear mapping curves. Does the MT6372 support more steps than this? In other words does it use a fourteen bit scale or does it use an 11-bit scale at a different register location? > + > + This driver can also be built as a module. If so, the module > + will be called "mt6370-backlight". > + > [...] > diff --git a/drivers/video/backlight/mt6370-backlight.c b/drivers/video/backlight/mt6370-backlight.c > new file mode 100644 > index 0000000..ba00a8f > --- /dev/null > +++ b/drivers/video/backlight/mt6370-backlight.c > [...] > +static int mt6370_bl_update_status(struct backlight_device *bl_dev) > +{ > + struct mt6370_priv *priv = bl_get_data(bl_dev); > + int brightness = backlight_get_brightness(bl_dev); > + unsigned int enable_val; > + u8 brightness_val[2]; > + int ret; > + > + if (brightness) { > + brightness_val[0] = (brightness - 1) & MT6370_BL_DIM2_MASK; > + brightness_val[1] = (brightness - 1) >> fls(MT6370_BL_DIM2_MASK); > + > + /* > + * To make MT6372 using 14 bits to control the brightness > + * backward compatible with 11 bits brightness control > + * (like MT6370 and MT6371 do), we left shift the value > + * and pad with 1 to remaining bits. Hence, the MT6372's > + * backlight brightness will be almost the same as MT6370's > + * and MT6371's. > + */ > + if (priv->vid_type == MT6370_VID_6372) { > + brightness_val[0] <<= MT6370_BL_DIM2_6372_SHIFT; > + brightness_val[0] |= MT6370_BL_DUMMY_6372_MASK; > + } This somewhat depends on the answer to the first question above, but what is the point of this shifting? If the range is 14-bit then the driver should set max_brightness to 16384 and present the full range of the MT6372 to the user. Especially when using linear mappings (which are a totally pointless scale to use for a backlight) the extra steps are useful for backlight animation. Daniel.