From patchwork Tue Jan 23 10:28:32 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Imre Deak X-Patchwork-Id: 13527148 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 4B09EC47DDB for ; Tue, 23 Jan 2024 10:28:48 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id EEBFA10E767; Tue, 23 Jan 2024 10:28:41 +0000 (UTC) Received: from mgamail.intel.com (mgamail.intel.com [192.55.52.115]) by gabe.freedesktop.org (Postfix) with ESMTPS id A450310E766; Tue, 23 Jan 2024 10:28:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1706005718; x=1737541718; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=oMNVZr1oLQvtaKFI0D5yAGpyJxKRX9F/sWObsoGIBLg=; b=Y5p51JeeOQRPiqaOItrD0tE/URwIqG76tncIjZBpPEnUlHysf2rL4d+/ ieUUBcz1D9XGGSzETpjCUod/l62ZcsUA9tWEAv7zZRgMm5domCdIjHkva Zsycxbq7lOGtMEmH/IWymoaIvxzmsnDgEx+rPdj3kechPGg3gsps49FUB UJ+K3rjvuOLwcSFJRaBC/gm0ou3JLIIlHUnL45yngSOfekhQQuPk7Rd73 FvQAiePbFYfHlwP1YfD4kbFxZVN10fBfyRUBHVvPJcobCpiDsMCCNKSg7 hIjtCEGeuqj8WtEzpexDUVM+bVludb4AvG+qQnYFX7TLiF3UZKm6YE/g/ g==; X-IronPort-AV: E=McAfee;i="6600,9927,10961"; a="401134091" X-IronPort-AV: E=Sophos;i="6.05,214,1701158400"; d="scan'208";a="401134091" Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by fmsmga103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Jan 2024 02:28:38 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10961"; a="856283360" X-IronPort-AV: E=Sophos;i="6.05,214,1701158400"; d="scan'208";a="856283360" Received: from ideak-desk.fi.intel.com ([10.237.72.78]) by fmsmga004-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Jan 2024 02:28:37 -0800 From: Imre Deak To: intel-gfx@lists.freedesktop.org Subject: [PATCH 01/19] drm/dp: Add drm_dp_max_dprx_data_rate() Date: Tue, 23 Jan 2024 12:28:32 +0200 Message-Id: <20240123102850.390126-2-imre.deak@intel.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20240123102850.390126-1-imre.deak@intel.com> References: <20240123102850.390126-1-imre.deak@intel.com> MIME-Version: 1.0 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: , Cc: dri-devel@lists.freedesktop.org Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Copy intel_dp_max_data_rate() to DRM core. It will be needed by a follow-up DP tunnel patch, checking the maximum rate the DPRX (sink) supports. Accordingly use the drm_dp_max_dprx_data_rate() name for clarity. This patchset will also switch calling the new DRM function in i915 instead of intel_dp_max_data_rate(). Signed-off-by: Imre Deak Reviewed-by: Uma Shankar --- drivers/gpu/drm/display/drm_dp_helper.c | 58 +++++++++++++++++++++++++ include/drm/display/drm_dp_helper.h | 2 + 2 files changed, 60 insertions(+) diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c index b1ca3a1100dab..24911243d4d3a 100644 --- a/drivers/gpu/drm/display/drm_dp_helper.c +++ b/drivers/gpu/drm/display/drm_dp_helper.c @@ -4058,3 +4058,61 @@ int drm_dp_bw_channel_coding_efficiency(bool is_uhbr) return 800000; } EXPORT_SYMBOL(drm_dp_bw_channel_coding_efficiency); + +/* + * Given a link rate and lanes, get the data bandwidth. + * + * Data bandwidth is the actual payload rate, which depends on the data + * bandwidth efficiency and the link rate. + * + * For 8b/10b channel encoding, SST and non-FEC, the data bandwidth efficiency + * is 80%. For example, for a 1.62 Gbps link, 1.62*10^9 bps * 0.80 * (1/8) = + * 162000 kBps. With 8-bit symbols, we have 162000 kHz symbol clock. Just by + * coincidence, the port clock in kHz matches the data bandwidth in kBps, and + * they equal the link bit rate in Gbps multiplied by 100000. (Note that this no + * longer holds for data bandwidth as soon as FEC or MST is taken into account!) + * + * For 128b/132b channel encoding, the data bandwidth efficiency is 96.71%. For + * example, for a 10 Gbps link, 10*10^9 bps * 0.9671 * (1/8) = 1208875 + * kBps. With 32-bit symbols, we have 312500 kHz symbol clock. The value 1000000 + * does not match the symbol clock, the port clock (not even if you think in + * terms of a byte clock), nor the data bandwidth. It only matches the link bit + * rate in units of 10000 bps. + * + * Note that protocol layers above the DPRX link level considered here can + * further limit the maximum data rate. Such layers are the MST topology (with + * limits on the link between the source and first branch device as well as on + * the whole MST path until the DPRX link) and (Thunderbolt) DP tunnels - + * which in turn can encapsulate an MST link with its own limit - with each + * SST or MST encapsulated tunnel sharing the BW of a tunnel group. + * + * TODO: Add support for querying the max data rate with the above limits as + * well. + * + * Returns the maximum data rate in kBps units. + */ +int drm_dp_max_dprx_data_rate(int max_link_rate, int max_lanes) +{ + int ch_coding_efficiency = + drm_dp_bw_channel_coding_efficiency(drm_dp_is_uhbr_rate(max_link_rate)); + int max_link_rate_kbps = max_link_rate * 10; + + /* + * UHBR rates always use 128b/132b channel encoding, and have + * 97.71% data bandwidth efficiency. Consider max_link_rate the + * link bit rate in units of 10000 bps. + */ + /* + * Lower than UHBR rates always use 8b/10b channel encoding, and have + * 80% data bandwidth efficiency for SST non-FEC. However, this turns + * out to be a nop by coincidence: + * + * int max_link_rate_kbps = max_link_rate * 10; + * max_link_rate_kbps = DIV_ROUND_DOWN_ULL(max_link_rate_kbps * 8, 10); + * max_link_rate = max_link_rate_kbps / 8; + */ + return DIV_ROUND_DOWN_ULL(mul_u32_u32(max_link_rate_kbps * max_lanes, + ch_coding_efficiency), + 1000000 * 8); +} +EXPORT_SYMBOL(drm_dp_max_dprx_data_rate); diff --git a/include/drm/display/drm_dp_helper.h b/include/drm/display/drm_dp_helper.h index 863b2e7add29e..454ae7517419a 100644 --- a/include/drm/display/drm_dp_helper.h +++ b/include/drm/display/drm_dp_helper.h @@ -813,4 +813,6 @@ int drm_dp_bw_overhead(int lane_count, int hactive, int bpp_x16, unsigned long flags); int drm_dp_bw_channel_coding_efficiency(bool is_uhbr); +int drm_dp_max_dprx_data_rate(int max_link_rate, int max_lanes); + #endif /* _DRM_DP_HELPER_H_ */