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Mon, 19 Oct 2026 07:45:25 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id 2CIxOpTK1WqrNAAAD6G6ig (envelope-from ); Mon, 19 Oct 2026 07:45:25 +0000 Message-ID: <23f0313d-8aba-43b9-80c4-678b970f8541@suse.de> Date: Mon, 19 Oct 2026 09:45:24 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] drm/format-helper: Add XRGB8888 to UYVY conversion To: Jie Feng Cc: dri-devel@lists.freedesktop.org, Maarten Lankhorst , Maxime Ripard , David Airlie , Simona Vetter , linux-kernel@vger.kernel.org References: <20261012170857.199561-1-hjf3108@gmail.com> <64707239-eac7-4259-a8ff-7ec43d13860e@suse.de> Content-Language: en-US From: Thomas Zimmermann Autocrypt: addr=tzimmermann@suse.de; keydata= xsBNBFs50uABCADEHPidWt974CaxBVbrIBwqcq/WURinJ3+2WlIrKWspiP83vfZKaXhFYsdg XH47fDVbPPj+d6tQrw5lPQCyqjwrCPYnq3WlIBnGPJ4/jreTL6V+qfKRDlGLWFjZcsrPJGE0 BeB5BbqP5erN1qylK9i3gPoQjXGhpBpQYwRrEyQyjuvk+Ev0K1Jc5tVDeJAuau3TGNgah4Yc hdHm3bkPjz9EErV85RwvImQ1dptvx6s7xzwXTgGAsaYZsL8WCwDaTuqFa1d1jjlaxg6+tZsB 9GluwvIhSezPgnEmimZDkGnZRRSFiGP8yjqTjjWuf0bSj5rUnTGiyLyRZRNGcXmu6hjlABEB AAHNJ1Rob21hcyBaaW1tZXJtYW5uIDx0emltbWVybWFubkBzdXNlLmRlPsLAjgQTAQgAOAIb AwULCQgHAgYVCgkICwIEFgIDAQIeAQIXgBYhBHIX+6yM6c9jRKFo5WgNwR1TC3ojBQJftODH AAoJEGgNwR1TC3ojx1wH/0hKGWugiqDgLNXLRD/4TfHBEKmxIrmfu9Z5t7vwUKfwhFL6hqvo lXPJJKQpQ2z8+X2vZm/slsLn7J1yjrOsoJhKABDi+3QWWSGkaGwRJAdPVVyJMfJRNNNIKwVb U6B1BkX2XDKDGffF4TxlOpSQzdtNI/9gleOoUA8+jy8knnDYzjBNOZqLG2FuTdicBXblz0Mf vg41gd9kCwYXDnD91rJU8tzylXv03E75NCaTxTM+FBXPmsAVYQ4GYhhgFt8S2UWMoaaABLDe 7l5FdnLdDEcbmd8uLU2CaG4W2cLrUaI4jz2XbkcPQkqTQ3EB67hYkjiEE6Zy3ggOitiQGcqp j//OwE0EWznS4AEIAMYmP4M/V+T5RY5at/g7rUdNsLhWv1APYrh9RQefODYHrNRHUE9eosYb T6XMryR9hT8XlGOYRwKWwiQBoWSDiTMo/Xi29jUnn4BXfI2px2DTXwc22LKtLAgTRjP+qbU6 3Y0xnQN29UGDbYgyyK51DW3H0If2a3JNsheAAK+Xc9baj0LGIc8T9uiEWHBnCH+RdhgATnWW GKdDegUR5BkDfDg5O/FISymJBHx2Dyoklv5g4BzkgqTqwmaYzsl8UxZKvbaxq0zbehDda8lv hFXodNFMAgTLJlLuDYOGLK2AwbrS3Sp0AEbkpdJBb44qVlGm5bApZouHeJ/+n+7r12+lqdsA EQEAAcLAdgQYAQgAIAIbDBYhBHIX+6yM6c9jRKFo5WgNwR1TC3ojBQJftOH6AAoJEGgNwR1T C3ojVSkIALpAPkIJPQoURPb1VWjh34l0HlglmYHvZszJWTXYwavHR8+k6Baa6H7ufXNQtThR yIxJrQLW6rV5lm7TjhffEhxVCn37+cg0zZ3j7zIsSS0rx/aMwi6VhFJA5hfn3T0TtrijKP4A SAQO9xD1Zk9/61JWk8OysuIh7MXkl0fxbRKWE93XeQBhIJHQfnc+YBLprdnxR446Sh8Wn/2D Ya8cavuWf2zrB6cZurs048xe0UbSW5AOSo4V9M0jzYI4nZqTmPxYyXbm30Kvmz0rYVRaitYJ 4kyYYMhuULvrJDMjZRvaNe52tkKAvMevcGdt38H4KSVXAylqyQOW5zvPc4/sq9c= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Flag: NO X-Spam-Score: -4.29 X-Spam-Level: X-Spamd-Result: default: False [-4.29 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; XM_UA_NO_VERSION(0.01)[]; TO_DN_SOME(0.00)[]; FREEMAIL_TO(0.00)[gmail.com]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; RCVD_TLS_ALL(0.00)[]; RCPT_COUNT_SEVEN(0.00)[7]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[lists.freedesktop.org,linux.intel.com,kernel.org,gmail.com,ffwll.ch,vger.kernel.org]; MID_RHS_MATCH_FROM(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,suse.com:url,suse.de:email] Hi Am 14.10.26 um 18:19 schrieb Jie Feng: > On Wed, 14 Oct 2026 at 17:03, Thomas Zimmermann wrote: >>>>>> ... >>>>>>> + v = drm_pixel_rgb2_to_v_bt601(r, g, b); >>>>>>> + u = drm_pixel_rgb2_to_u_bt601(r, g, b); >>>>>>> + >>>>>>> + transfer_buffer[dst_offset++] = u; >>>>>>> + transfer_buffer[dst_offset++] = y1; >>>>>>> + transfer_buffer[dst_offset++] = v; >>>>>>> + transfer_buffer[dst_offset++] = y2; >>>>>> Rather that writing bytes individually, use put_unaligned_le32() or a >>>>>> similar helper. Byte order within a pixel is little endian, although >>>>>> I'm not sure what this means for UYVY. >>>>> This is meant to be sent over a usb transfer, so byte order needs to be >>>>> the same on both little and big endian systems. >>>> DRM formats always refer to little endian. As it is implemented now, >>>> it's not clear what the endianess of your output is. Please duplicate >>>> the other helpers' logic. They all pack the output with appropriate >>>> helpers. If the USB device requires BE, you have to write a separate >>>> conversion helper for that. >>>> >>>> BTW, you have an OOB access if the line width is not a multiple of 2. >>> How should I handle this? Rounding it within the helper doesn't seem >>> to make sense and the function return is a void, so it can't return -EINVAL. >> It's the callers responsibility to pass in enough pixels. You'll have to >> take care of it in the driver by rounding the damage area accordingly. >> It's not optimal but it's not a big deal either. >> >> In the line-conversion helper, simply round down to the nearest multiple >> of 2. > Yes, that is already done in my driver. > >>> Other helpers ignore the -ENOMEM error when drm_format_conv_state_reserve >>> fails, so should it follow this convention? >> Do you have a specific example? > The call chain goes like this: > drm_fb_xrgb8888_to_rgb888 > drm_fb_xfrm > __drm_fb_xfrm: > stmp = drm_format_conv_state_reserve(state, sbuf_len, GFP_KERNEL); > if (!stmp) > return -ENOMEM; > > Since drm_fb_xrgb8888_to_rgb888 is a void, it calls drm_fb_xfrm without > checking for the return value. Similarly for other drm_fb_xrgb8888_to* > functions. For the uyvy helper it could just return without > doing any work if it is not a multiple of 2, like in the -ENOMEM case. Ok, that's what you mean.  We run these conversion functions in atomic_update, when it's too late to do anything with the return value. So we drop the return value. You should rather not return an error if the width is not a multiple of 2. Even then, there's some data available for output to the user. Errors and problems need to be detected by atomic_check, prepare_fb or a similar callback that runs before atomic_update. Best regards Thomas > >>> Alternatively, drm_fb_xfrm can be exported, and let the driver define >>> the rgb->yuv coefficients? But I think it is fine since _to_gray8 also >>> cites BT.601. >> The current constants seem fine. With the 2-pixel alignment, there >> shouldn't be any other cases required. >> >> Best regards >> Thomas >> >> >> >> -- >> -- >> Thomas Zimmermann >> Graphics Driver Developer >> SUSE Software Solutions Germany GmbH >> Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com >> GF: Stefan Gaiser, Jochen Jaser, Abhinav Puri, (HRB 36809, AG Nürnberg) >> >> -- -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com GF: Stefan Gaiser, Jochen Jaser, Abhinav Puri, (HRB 36809, AG Nürnberg)