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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spamd-Result: default: False [-4.30 / 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]; ARC_NA(0.00)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; MIME_TRACE(0.00)[0:+]; RCPT_COUNT_TWELVE(0.00)[17]; FREEMAIL_TO(0.00)[huawei.com,oss.qualcomm.com,hisilicon.com,linaro.org,linux.intel.com,kernel.org,gmail.com,ffwll.ch]; RCVD_VIA_SMTP_AUTH(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_TLS_ALL(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[bootlin.com:url, suse.com:url, imap1.dmz-prg2.suse.org:helo, suse.de:mid] X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Hi Am 06.05.26 um 10:56 schrieb Yongbang Shi: >> Hi, >> >> sorry for the late reply. I'm fairly busy. >> > Thank you so much for taking the time to review our code. No worries at all—we'd really appreciate it if you could take > a look whenever you have time. > >> Am 28.04.26 um 14:53 schrieb Yongbang Shi: >>>> Hi >>>> >>>> Am 28.04.26 um 05:58 schrieb Yongbang Shi: >>>> [...] >>>>>> There's a problem with the overall logic here: if the physical status is 'connected' and the helper could not retrieve >>>>>> any modes, the helper should return 0 here. Then the DRM helpers do the right thing with setting up a few modes or an >>>>>> EDID override as a fallback. See [2]. For example, on my broken test system, I'd be able to provide my display's EDID >>>>>> and get the correct output. >>>>>> >>>>>> [2] https://elixir.bootlin.com/linux/v7.0.1/source/drivers/gpu/drm/drm_probe_helper.c#L436 >>>>>> >>>>>> Any code below is BMC setup and should run in an else branch, just like in ast. >>>>>> >>>>> The `drm_edid_override_connector_update` interface is used to retrieve an overridden EDID from debugfs or from >>>>> firmware: >>>>>     * Debugfs: Requires the user to manually perform file operations to configure it; >>>>>     * Firmware: Requires the distribution’s operating system or the user to place the EDID binary file in the >>>>>                 `/lib/firmware/` directory, and the `drm.edid_firmware` parameter must be specified in the GRUB boot >>>>>                 parameters; >>>>> >>>>> The modification method you provided allows for display even when the EDID cannot be retrieved. But both of these >>>>> methods require cooperation from the user or the distribution's operating system, making implementation relatively >>>>> difficult. >>>> Yes, it's the established way for users to override the EDID. >>>> >>>>> Our use case requires that the KVM's display functionality remain intact even when no VGA or DisplayPort monitor is >>>>> connected. I believe setting `drm_set_preferred_mode` (1024x768) as the default resolution when no monitor is present >>>>> would be a more universal solution. Similarly, on your test system, this approach would ensure basic display >>>>> functionality. >>>> If no modes could be detected on the VGA and no EDID has been provided by the user, DRM helpers will install a set of >>>> default modes that are suitable for graphics cards. See [1]. The modes installed for the KVM are not all compatible with >>>> VGA.  If you rely on DRM helpers, you'll always get correct modes for VGA and KVM. >>>> >>>> Generally speaking, the decision of VGA-vs-KVM should be in ->detect. Having phys_state/phys_status does this very well. >>>> The ->get_modes function should then use whatever has been detected. >>>> >>>> [1] https://elixir.bootlin.com/linux/v7.0.1/source/drivers/gpu/drm/drm_probe_helper.c#L653 >>>> >>> Yes, I understand what you mean. But there's another issue here; we've also tested the scenario where we directly return >>> 0. However, we found that only three resolutions remain supported: 1024*768, 800*600 and 640*480. This is because the >>> resolution added via `drm_add_modes_noedid` in the helper has a maximum of 1024*768. This doesn't look good—there are >>> too few resolutions available for users to choose from in KVM. >>> >>> With the current implementation, when `count == 0`, we set the resolution to the highest resolution supported by our >>> CRTC, allowing users more options. >> But why do you second-guess the results from ->detect?  Th call to ->detect already established that there's a display >> connected.  If ->get_modes cannot find useful modes, then don't treat it as a BMC now. Return 0 and let DRM choose some >> same defaults.  These 3 low-res modes act as a safe base line. Reporting high-res BMC modes might accidentally fry >> someone's monitor. >> > Sorry, my mistake. My previous reply was not quite right. I'm a little confused about this situation. I focused on > optimizing the KVM display when no monitor is connected, but when no monitor is connected, `vdac->phys_status` is set to > `disconnected`. Following the AST implementation you recommended[1], it takes the `else` branch and sets a custom list. > > `vdac->phys_state == connected` and `drm_connector_helper_get_modes` returns 0, in this case, either the returned EDID > does not match any available options, or there is an issue with the display. In such situations, it's good to let DRM > choose some defaults. > > I will follow the AST implementation[1] to make the modification in v6. > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpu/drm/ast/ast_vga.c?h=v7.1-rc2#L31 > >>> Of course, this implementation has its drawbacks; it doesn't allow users to provide a custom resolution list via debugfs >>> using the override method when `count == 0`. But this method isn't very important for how our product is used. >> The upstream Linux kernel is not a product, but a shared commodity. It needs to work in everyone's best interest. >> > Yes, we'll keep that in mind; when developing community code, we should consider the overall architecture. > > Thanks, > Yongbang. Sounds good. Looking forward to the next revision. Best regards Thomas > >> Best regards >> Thomas >> >>> Thanks, >>> Yongbang. >>> >>>> Best regards >>>> Thomas >>>> >>>>>>>     +    drm_edid_connector_update(connector, NULL); >>>>>>>         count = drm_add_modes_noedid(connector, >>>>>>>                          connector->dev->mode_config.max_width, >>>>>>>                          connector->dev->mode_config.max_height); >>>>>>>         drm_set_preferred_mode(connector, 1024, 768); >>>>>>>     -out: >>>>>>> -    drm_edid_free(drm_edid); >>>>>>> - >>>>>>>         return count; >>>>>>>     } >>>>>>>     @@ -57,10 +50,32 @@ static void hibmc_connector_destroy(struct drm_connector *connector) >>>>>>>         drm_connector_cleanup(connector); >>>>>>>     } >>>>>>>     +static int hibmc_vdac_detect(struct drm_connector *connector, >>>>>>> +                 struct drm_modeset_acquire_ctx *ctx, >>>>>>> +                 bool force) >>>>>>> +{ >>>>>>> +    struct hibmc_drm_private *priv = to_hibmc_drm_private(connector->dev); >>>>>>> +    int state = drm_connector_helper_detect_from_ddc(connector, ctx, >>>>>>> +                             force); >>>>>> 'state' -> 'status' >>>>>> >>>>> Okay. >>>>> >>>>>>> +    struct hibmc_vdac *vdac = to_hibmc_vdac(connector); >>>>>>> + >>>>>>> +    if (priv->dp.phys_state == connector_status_connected) >>>>>>> +        return vdac->phys_state = state; >>>>>> Please only one statement per line. First assign, then return. >>>>>> >>>>> Yes, Sorry about that. According to the Linux kernel coding guidelines, this line of code should be split. >>>>> >>>>> >>>>> Thanks, >>>>> Yongbang. >>>>> >>>>>>> + >>>>>>> +    if (state != vdac->phys_state) >>>>>>> +        ++connector->epoch_counter; >>>>>>> +    vdac->phys_state = state; >>>>>>> + >>>>>>> +    /* If both the DP and VDAC physical states are disconnected, >>>>>>> +     * the "connected" status is returned to support KVM display. >>>>>>> +     */ >>>>>>> +    return connector_status_connected; >>>>>> I haven't tried, but I think this should also resolve the problems on my test systems. Great, thanks a lot! I might >>>>>> just >>>>>> get default resolutions for now, but that's OK. >>>>>> >>>>>> Best regards >>>>>> Thomas >>>>>> >>>>>>> +} >>>>>>> + >>>>>>>     static const struct drm_connector_helper_funcs >>>>>>>         hibmc_connector_helper_funcs = { >>>>>>>         .get_modes = hibmc_connector_get_modes, >>>>>>> -    .detect_ctx = drm_connector_helper_detect_from_ddc, >>>>>>> +    .detect_ctx = hibmc_vdac_detect, >>>>>>>     }; >>>>>>>       static const struct drm_connector_funcs hibmc_connector_funcs = { >>>>>>> @@ -130,6 +145,8 @@ int hibmc_vdac_init(struct hibmc_drm_private *priv) >>>>>>>           connector->polled = DRM_CONNECTOR_POLL_CONNECT | DRM_CONNECTOR_POLL_DISCONNECT; >>>>>>>     +    vdac->phys_state = connector_status_connected; >>>>>>> + >>>>>>>         return 0; >>>>>>>       err: -- -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)