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Mon, 14 Mar 2022 07:07:46 -0700 (PDT) X-Google-Smtp-Source: ABdhPJxUmZKMWpb2vbN6Fu8O0zteEWAjmmY/DHvyxw4A1qQVFF+i6VWRfQ9qS5Kjt/nNczT10/+Vzw== X-Received: by 2002:a5d:6daf:0:b0:203:8214:ae65 with SMTP id u15-20020a5d6daf000000b002038214ae65mr16784102wrs.145.1647266865920; Mon, 14 Mar 2022 07:07:45 -0700 (PDT) Received: from [192.168.1.102] ([92.176.231.205]) by smtp.gmail.com with ESMTPSA id v10-20020a05600c214a00b00389bcc75559sm15441665wml.27.2022.03.14.07.07.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 14 Mar 2022 07:07:45 -0700 (PDT) Message-ID: <9b8bbc6a-e499-99c7-8fe6-95c4256ef61d@redhat.com> Date: Mon, 14 Mar 2022 15:07:43 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Subject: Re: [PATCH 2/4] drm/format-helper: Add drm_fb_gray8_to_mono_reversed() Content-Language: en-US To: Geert Uytterhoeven Cc: Linux Kernel Mailing List , Linux Fbdev development list , Maxime Ripard , Daniel Vetter , Andy Shevchenko , DRI Development , =?UTF-8?Q?Noralf_Tr=c3=b8nnes?= , Daniel Vetter , David Airlie , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann References: <20220131201225.2324984-1-javierm@redhat.com> <20220131201225.2324984-3-javierm@redhat.com> From: Javier Martinez Canillas In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello Geert, On 3/14/22 14:40, Geert Uytterhoeven wrote: > Hi Javier, > > On Mon, Jan 31, 2022 at 9:12 PM Javier Martinez Canillas > wrote: >> Add support to convert 8-bit grayscale to reversed monochrome for drivers >> that control monochromatic displays, that only have 1 bit per pixel depth. >> >> This helper function was based on repaper_gray8_to_mono_reversed() from >> the drivers/gpu/drm/tiny/repaper.c driver. >> >> Signed-off-by: Javier Martinez Canillas > >> --- a/drivers/gpu/drm/drm_format_helper.c >> +++ b/drivers/gpu/drm/drm_format_helper.c >> @@ -584,3 +584,38 @@ int drm_fb_blit_toio(void __iomem *dst, unsigned int dst_pitch, uint32_t dst_for >> return -EINVAL; >> } >> EXPORT_SYMBOL(drm_fb_blit_toio); >> + >> +/** >> + * drm_fb_gray8_to_mono_reversed - Convert grayscale to reversed monochrome >> + * @dst: reversed monochrome destination buffer > > What's the meaning of "reversed"? Originally I took this helper from the repaper driver and it was called repaper_gray8_to_mono_reversed(), so the naming just got carried over. > During the last few days, I've been balancing between (a) "reverse > video" and (b) "reverse bit order", but none of them seems to be true. > > (a) The code maps 0-127 to 0 and 8-255 to 1, which just reduces from > 256 to 2 grayscale levels, without inversion. The result is also > white-on-black on my ssd130x OLED. > (b) On little-endian, the CFB drawops use little-endian bit order, > which is what ends up in "byte" in the code below. > As far as I understand is (a) from the options since the repaper display uses black-on-white. But as you pointed out the ssd130x OLEDs instead do white-on-black. I should had probably just name the helper drm_fb_gray8_to_monochrome() or maybe drm_fb_gray8_to_gray1() ? -- Best regards, Javier Martinez Canillas Linux Engineering Red Hat