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[122.59.250.182]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-39d951d6b08sm2884821a91.8.2026.09.10.21.53.19 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Thu, 10 Sep 2026 21:53:26 -0700 (PDT) Subject: Re: [PATCH] fbdev: atafb: Restrict SuperBlitter to supported formats To: Geert Uytterhoeven References: <20260827093948.2825531-1-lilinmao@kylinos.cn> <4f3c7184-1b5c-4074-b8a1-49261833df8f@gmail.com> Cc: =?UTF-8?B?TWlybyBLcm9ww6HEjWVr?= , Linmao Li , deller@gmx.de, linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org From: Michael Schmitz Message-ID: Date: Fri, 11 Sep 2026 16:53:16 +1200 User-Agent: Mozilla/5.0 (X11; Linux ppc; rv:45.0) Gecko/20100101 Icedove/45.4.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Hi Geert, Am 08.09.2026 um 19:18 schrieb Geert Uytterhoeven: >>> Unless I overlooked something, the fill also looks wrong on paper: the >>> first line is filled with a repeated byte and then with repeated >>> 32-bit words of the same value, which cannot reproduce a 3-byte pixel >>> pattern unless all three bytes are equal. >> >> You're correct - we'd need a memset24() to account for that. Without > > Unless the frame buffer would be using a DIRECT_COLOR visual (which > is not the case), then you could draw pixels in the 16 console colors > by replicating the color index in all 3 bytes ;-) Sorry, I don't get that - are the console colors chosen judiciously to allow for that? >> hardware support this is an academic exercise that I don't have time for :-) > > True. And as this code is used only to fill the first line (the blitter > replicates it into the other lines), the performance difference between > a simple byte loop and a true memset24() won't be that large. I wasn't worried about performance as the blitter takes care of most of the work (though we may schedule away from svblit_fillrect() while the blitter is active). Getting the 'simple byte loop' right is more important. My sample code got everything wrong in fact. There's a reason why we don't work with 24 bit sized objects usually, and probably a reason why 24 bpp was never implemented for the SuperVidel :-) Cheers, Michael > > > Gr{oetje,eeting}s, > > Geert >