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Message-ID: <1f599b97-9242-3844-4372-1610948f4baf@quicinc.com>
Date:   Sun, 2 Oct 2022 16:30:30 -0700
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Subject: Re: [PATCH v4 10/14] gunyah: sysfs: Add node to describe supported
 features
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To:     Joe Perches <joe@perches.com>,
        Elliot Berman <quic_eberman@quicinc.com>,
        Bjorn Andersson <quic_bjorande@quicinc.com>
CC:     Murali Nalajala <quic_mnalajal@quicinc.com>,
        Trilok Soni <quic_tsoni@quicinc.com>,
        Srivatsa Vaddagiri <quic_svaddagi@quicinc.com>,
        Carl van Schaik <quic_cvanscha@quicinc.com>,
        Andy Gross <agross@kernel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
        Jassi Brar <jassisinghbrar@gmail.com>,
        <linux-arm-kernel@lists.infradead.org>,
        "Mark Rutland" <mark.rutland@arm.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Sudeep Holla <sudeep.holla@arm.com>,
        "Marc Zyngier" <maz@kernel.org>, Rob Herring <robh+dt@kernel.org>,
        "Krzysztof Kozlowski" <krzysztof.kozlowski+dt@linaro.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Will Deacon <will@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        <devicetree@vger.kernel.org>, <linux-doc@vger.kernel.org>,
        <linux-arm-msm@vger.kernel.org>, <linux-kernel@vger.kernel.org>
References: <20220928195633.2348848-1-quic_eberman@quicinc.com>
 <20220928195633.2348848-11-quic_eberman@quicinc.com>
 <3c02aad6d8bde70964b403a3cb8004de969becc6.camel@perches.com>
From:   Jeff Johnson <quic_jjohnson@quicinc.com>
In-Reply-To: <3c02aad6d8bde70964b403a3cb8004de969becc6.camel@perches.com>
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On 9/29/2022 12:36 AM, Joe Perches wrote:
> On Wed, 2022-09-28 at 12:56 -0700, Elliot Berman wrote:
>> Add a sysfs node to list the features that the Gunyah hypervisor and
>> Linux supports. For now, Linux support cspace (capability IDs) and
>> message queues, so only report those..
> []
>> diff --git a/drivers/virt/gunyah/sysfs.c b/drivers/virt/gunyah/sysfs.c
> []
>> @@ -25,9 +25,24 @@ static ssize_t variant_show(struct kobject *kobj, struct kobj_attribute *attr, c
>>   }
>>   static struct kobj_attribute variant_attr = __ATTR_RO(variant);
>>   
>> +static ssize_t features_show(struct kobject *kobj, struct kobj_attribute *attr, char *buffer)
>> +{
>> +	int len = 0;
>> +
>> +	if (GH_IDENTIFY_PARTITION_CSPACE(gunyah_api.flags))
>> +		len += sysfs_emit_at(buffer, len, "cspace ");
>> +	if (GH_IDENTIFY_MSGQUEUE(gunyah_api.flags))
>> +		len += sysfs_emit_at(buffer, len, "message-queue ");
>> +
>> +	len += sysfs_emit_at(buffer, len, "\n");
>> +	return len;
>> +}
> 
> It's generally nicer to avoid unnecessary output spaces.
> 
> Perhaps:
> 
> {
> 	int len = 0;
> 
> 	if (GH_IDENTIFY_PARTITION_CSPACE(gunyah_api.flags))
> 		len += sysfs_emit_at(buffer, len, "cspace");
> 	if (GH_IDENTIFY_MSGQUEUE(gunyah_api.flags)) {
> 		if (len)
> 			len += sysfs_emit_at(buffer, len, " ");
> 		len += sysfs_emit_at(buffer, len, "message-queue");
> 	}
> 
> 	len += sysfs_emit_at(buffer, len, "\n");
> 
> 	return len;
> }
> 

that approach seems ok for 2 features, but imo doesn't scale for more.
I like the original code with one exception:

	if (GH_IDENTIFY_PARTITION_CSPACE(gunyah_api.flags))
		len += sysfs_emit_at(buffer, len, "cspace ");
	if (GH_IDENTIFY_MSGQUEUE(gunyah_api.flags))
		len += sysfs_emit_at(buffer, len, "message-queue ");

	/* overwrite last trailing space */
	if (len)
		len--;

	len += sysfs_emit_at(buffer, len, "\n");
	return len;