From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from pv50p00im-ztdg10011901.me.com (pv50p00im-ztdg10011901.me.com [17.58.6.50]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 77DD119D88C for ; Tue, 27 Aug 2024 11:54:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=17.58.6.50 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724759650; cv=none; b=KMiDgF8DAVByL6V+L79u4AN1LfHbqjAKgwAkOtcA8mAskDIX5G8+TgqksXjUzpkEC1ednTny8aH20Lu/cXg8gsNVRkKvGA3ZtHklQSGV92z2oFuKCiRWrs5QCJrfl+B/mV/Mvi4iDZcFG1IJdS5BjbNJo/SbVTXtWwwE9MKV+cE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724759650; c=relaxed/simple; bh=nEi8II45wAmL1f5XTIWsbyTtcx8NX0c09t6x4DVix6A=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=GfSi24HYYCYku+u1mw2A0nxM7/qP7qx7V9UkORFjJoPTeaJgdnuiBhuihWKCmoy0Y3e8lR3FhBh3YrRN9eHph3MQNwu420usjtMX9YAS+tgWXMYtnYiYZFxvr7OI7GU5jWDK9nk6T0yiHCYPeY0iPckeQAZ4/Y9m/EaVXiY9lb4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=icloud.com; spf=pass smtp.mailfrom=icloud.com; dkim=pass (2048-bit key) header.d=icloud.com header.i=@icloud.com header.b=zOzev3E+; arc=none smtp.client-ip=17.58.6.50 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=icloud.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=icloud.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=icloud.com header.i=@icloud.com header.b="zOzev3E+" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=icloud.com; s=1a1hai; t=1724759649; bh=OYrHNLwmvHe2oa0rD8JJuTUs4ODsC2IJMqoKI314ldc=; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; b=zOzev3E+mosk3j16HL4HiEHL5WWqXUvHyj+nqVG/LPaaLQZRkO/seWBBb5BOOhchn O8MU75aMMqEEYO85vpySf8LxFn8N/b43eXisXvYRgH+QJU/0WExah46MmVzN9K1X48 eb9NV60IlxYNaiRXPck10Ma9wo4ObI2DfJaQTEShk6Qjyvv9/tzEh9bdetfRkGQYIT EfFwSR4zeMoBe+zKTu4R0r+LCH8Cdr/Re0/DjjHX3XqpDbrjnHxBnASU5tAPwoQmhS Eeo37doe9R1qcHVXLWqFnTGzz3zUx8F64fmjjPetf/zgqiLHxrM5+Ny6OsdkusmJUN Pg5Rzlw8tC8gg== Received: from [192.168.1.26] (pv50p00im-dlb-asmtp-mailmevip.me.com [17.56.9.10]) by pv50p00im-ztdg10011901.me.com (Postfix) with ESMTPSA id DDCA83A008D; Tue, 27 Aug 2024 11:53:59 +0000 (UTC) Message-ID: Date: Tue, 27 Aug 2024 19:53:55 +0800 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/3] cxl/region: Find free cxl decoder by device_for_each_child() To: Jonathan Cameron Cc: Greg Kroah-Hartman , "Rafael J. Wysocki" , Davidlohr Bueso , Dave Jiang , Alison Schofield , Vishal Verma , Ira Weiny , Dan Williams , Takashi Sakamoto , Timur Tabi , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , linux-kernel@vger.kernel.org, linux-cxl@vger.kernel.org, netdev@vger.kernel.org, Zijun Hu References: <20240824-const_dfc_prepare-v3-0-32127ea32bba@quicinc.com> <20240824-const_dfc_prepare-v3-2-32127ea32bba@quicinc.com> <20240827123006.00004527@Huawei.com> Content-Language: en-US From: Zijun Hu In-Reply-To: <20240827123006.00004527@Huawei.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Proofpoint-ORIG-GUID: zXSu555QJvhB-nSvhZ59A5Eowv9iK99L X-Proofpoint-GUID: zXSu555QJvhB-nSvhZ59A5Eowv9iK99L X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.272,Aquarius:18.0.1039,Hydra:6.0.680,FMLib:17.12.28.16 definitions=2024-08-27_06,2024-08-27_01,2024-05-17_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 malwarescore=0 mlxlogscore=999 clxscore=1015 adultscore=0 suspectscore=0 bulkscore=0 phishscore=0 spamscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2308100000 definitions=main-2408270087 On 2024/8/27 19:30, Jonathan Cameron wrote: > On Sat, 24 Aug 2024 17:07:44 +0800 > Zijun Hu wrote: > >> From: Zijun Hu >> >> To prepare for constifying the following old driver core API: >> >> struct device *device_find_child(struct device *dev, void *data, >> int (*match)(struct device *dev, void *data)); >> to new: >> struct device *device_find_child(struct device *dev, const void *data, >> int (*match)(struct device *dev, const void *data)); >> >> The new API does not allow its match function (*match)() to modify >> caller's match data @*data, but match_free_decoder() as the old API's >> match function indeed modifies relevant match data, so it is not suitable >> for the new API any more, solved by using device_for_each_child() to >> implement relevant finding free cxl decoder function. >> >> Suggested-by: Ira Weiny >> Signed-off-by: Zijun Hu > This seems to functionally do the same as before. > yes, this change have the same logic as previous existing logic. > I'm not sure I like the original code though so a comment inline. > >> --- >> drivers/cxl/core/region.c | 30 ++++++++++++++++++++++++------ >> 1 file changed, 24 insertions(+), 6 deletions(-) >> >> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c >> index 21ad5f242875..c2068e90bf2f 100644 >> --- a/drivers/cxl/core/region.c >> +++ b/drivers/cxl/core/region.c >> @@ -794,10 +794,15 @@ static size_t show_targetN(struct cxl_region *cxlr, char *buf, int pos) >> return rc; >> } >> >> +struct cxld_match_data { >> + int id; >> + struct device *target_device; >> +}; >> + >> static int match_free_decoder(struct device *dev, void *data) >> { >> + struct cxld_match_data *match_data = data; >> struct cxl_decoder *cxld; >> - int *id = data; >> >> if (!is_switch_decoder(dev)) >> return 0; >> @@ -805,17 +810,31 @@ static int match_free_decoder(struct device *dev, void *data) >> cxld = to_cxl_decoder(dev); >> >> /* enforce ordered allocation */ >> - if (cxld->id != *id) >> + if (cxld->id != match_data->id) > > Why do we carry on in this case? > Conditions are: > 1. Start match_data->id == 0 > 2. First pass cxld->id == 0 (all good) or > cxld->id == 1 say (and we skip until we match > on cxld->id == 0 (perhaps on the second child if they are > ordered (1, 0, 2) etc. > > If we skipped and then matched on second child but it was > already in use (so region set), we will increment match_data->id to 1 > but never find that as it was the one we skipped. > > So this can only work if the children are ordered. > So if that's the case and the line above is just a sanity check > on that, it should be noisier (so an error print) and might > as well fail as if it doesn't match all bets are off. > it seems Ira Weiny also has some concerns related to previous existing logic as following: https://lore.kernel.org/all/66c4a136d9764_2ddc2429435@iweiny-mobl.notmuch/ "Also for those working on CXL I'm questioning the use of ID here and the dependence on the id's being added to the parent in order. Is that a guarantee?" perhaps, create a new dedicated thread to discuss original design. > Jonathan > >> return 0; >> >> - if (!cxld->region) >> + if (!cxld->region) { >> + match_data->target_device = get_device(dev); >> return 1; >> + } >> >> - (*id)++; >> + match_data->id++; >> >> return 0; >> } >> >> +/* NOTE: need to drop the reference with put_device() after use. */ >> +static struct device *find_free_decoder(struct device *parent) >> +{ >> + struct cxld_match_data match_data = { >> + .id = 0, >> + .target_device = NULL, >> + }; >> + >> + device_for_each_child(parent, &match_data, match_free_decoder); >> + return match_data.target_device; >> +} >> + >> static int match_auto_decoder(struct device *dev, void *data) >> { >> struct cxl_region_params *p = data; >> @@ -840,7 +859,6 @@ cxl_region_find_decoder(struct cxl_port *port, >> struct cxl_region *cxlr) >> { >> struct device *dev; >> - int id = 0; >> >> if (port == cxled_to_port(cxled)) >> return &cxled->cxld; >> @@ -849,7 +867,7 @@ cxl_region_find_decoder(struct cxl_port *port, >> dev = device_find_child(&port->dev, &cxlr->params, >> match_auto_decoder); >> else >> - dev = device_find_child(&port->dev, &id, match_free_decoder); >> + dev = find_free_decoder(&port->dev); >> if (!dev) >> return NULL; >> /* >> >