From mboxrd@z Thu Jan 1 00:00:00 1970 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 A8C3EC4332F for ; Thu, 9 Nov 2023 20:36:03 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 3D59410E909; Thu, 9 Nov 2023 20:35:25 +0000 (UTC) Received: from mgamail.intel.com (mgamail.intel.com [192.55.52.136]) by gabe.freedesktop.org (Postfix) with ESMTPS id E0D0710E909; Thu, 9 Nov 2023 20:35:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1699562117; x=1731098117; h=date:from:to:cc:subject:message-id:references: mime-version:content-transfer-encoding:in-reply-to; bh=kBsCSBnWQCB51hsV05oddKau35cCLo6WCL8eUx470rw=; b=m1ouIe2mUcuRbOs6PCBDWn5voSgaIwz364A5wRH+WGQhijNp3K3nZD+k LOycZovFHXO1t38HCQ65B9aXEZOgICwyzl1MIUwDDs7i+7dmEXNS7L5eb 5fQFgbuHF76GvJJv0TAGwhrKtk79r8OP2TCKP7e7Waq9JvSIo3O72XEzw ticvuMffkbr86d9SAKm52CYANvoMpRvS2QkKzF22jveJD9CecZOFJy2F/ YhuzeIcBkZkKlxCYaIQ1GeYmJlWXw+1WUXl7WKt065vGDQkiTkATJl2Xt rGFg7/8HXQGztQqdOWK9GYEkJp78ORtADQbrSlSnmtpv/VTDZHuQAC9xc w==; X-IronPort-AV: E=McAfee;i="6600,9927,10889"; a="369405613" X-IronPort-AV: E=Sophos;i="6.03,290,1694761200"; d="scan'208";a="369405613" Received: from orsmga007.jf.intel.com ([10.7.209.58]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 09 Nov 2023 12:35:16 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10889"; a="757001599" X-IronPort-AV: E=Sophos;i="6.03,290,1694761200"; d="scan'208";a="757001599" Received: from stinkpipe.fi.intel.com (HELO stinkbox) ([10.237.72.74]) by orsmga007.jf.intel.com with SMTP; 09 Nov 2023 12:35:13 -0800 Received: by stinkbox (sSMTP sendmail emulation); Thu, 09 Nov 2023 22:35:12 +0200 Date: Thu, 9 Nov 2023 22:35:12 +0200 From: Ville =?iso-8859-1?Q?Syrj=E4l=E4?= To: "Belgaumkar, Vinay" Message-ID: References: <20231109192148.475156-1-vinay.belgaumkar@intel.com> <72f09667-24d5-403a-ba9a-3465c681fec3@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <72f09667-24d5-403a-ba9a-3465c681fec3@intel.com> X-Patchwork-Hint: comment Subject: Re: [Intel-gfx] [PATCH] drm/i915: Read a shadowed mmio register for ggtt flush X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On Thu, Nov 09, 2023 at 12:01:26PM -0800, Belgaumkar, Vinay wrote: > > On 11/9/2023 11:30 AM, Ville Syrjälä wrote: > > On Thu, Nov 09, 2023 at 11:21:48AM -0800, Vinay Belgaumkar wrote: > >> We read RENDER_HEAD as a part of the flush. If GT is in > >> deeper sleep states, this could lead to read errors since we are > >> not using a forcewake. Safer to read a shadowed register instead. > > IIRC shadowing is only thing for writes, not reads. > > Sure, but reading from a shadowed register does return the cached value Does it? I suppose that would make some sense, but I don't recall that ever being stated anywhere. At least before the shadow registers existed reads would just give you zeroes when not awake. > (even though we don't care about the vakue here). When GT is in deeper > sleep states, it is better to read a shadowed (cached) value instead of > trying to attempt an mmio register read without a force wake anyways. So you're saying reads from non-shadowed registers fails somehow when not awake? How exactly do they fail? And when reading from a shadowed register that failure never happens? > > Thanks, > > Vinay. > > > > >> Cc: John Harrison > >> Cc: Daniele Ceraolo Spurio > >> Signed-off-by: Vinay Belgaumkar > >> --- > >> drivers/gpu/drm/i915/gt/intel_gt.c | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/drivers/gpu/drm/i915/gt/intel_gt.c b/drivers/gpu/drm/i915/gt/intel_gt.c > >> index ed32bf5b1546..ea814ea5f700 100644 > >> --- a/drivers/gpu/drm/i915/gt/intel_gt.c > >> +++ b/drivers/gpu/drm/i915/gt/intel_gt.c > >> @@ -451,7 +451,7 @@ void intel_gt_flush_ggtt_writes(struct intel_gt *gt) > >> > >> spin_lock_irqsave(&uncore->lock, flags); > >> intel_uncore_posting_read_fw(uncore, > >> - RING_HEAD(RENDER_RING_BASE)); > >> + RING_TAIL(RENDER_RING_BASE)); > >> spin_unlock_irqrestore(&uncore->lock, flags); > >> } > >> } > >> -- > >> 2.38.1 -- Ville Syrjälä Intel