Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Received-SPF: Pass (protection.outlook.com: domain of nvidia.com designates
 216.228.112.34 as permitted sender) receiver=protection.outlook.com;
 client-ip=216.228.112.34; helo=mail.nvidia.com;
Subject: Re: [RFC 08/11] gpiolib: cdev: Add hardware timestamp clock type
To:     Linus Walleij <linus.walleij@linaro.org>
CC:     "thierry.reding@gmail.com" <thierry.reding@gmail.com>,
        Jon Hunter <jonathanh@nvidia.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-tegra <linux-tegra@vger.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@baylibre.com>,
        Kent Gibson <warthog618@gmail.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>,
        Linux Doc Mailing List <linux-doc@vger.kernel.org>,
        Rob Herring <robh+dt@kernel.org>
References: <20210625235532.19575-1-dipenp@nvidia.com>
 <20210625235532.19575-9-dipenp@nvidia.com>
 <CACRpkdb-AFvLhwOLSs5ocqiZ6ZwZbQMzWGfQ6C3AX+=ouH+=ng@mail.gmail.com>
From:   Dipen Patel <dipenp@nvidia.com>
Message-ID: <2bfbb684-d9d3-8779-11fe-6b4152f114d6@nvidia.com>
Date:   Thu, 29 Jul 2021 20:16:04 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.11.0
MIME-Version: 1.0
In-Reply-To: <CACRpkdb-AFvLhwOLSs5ocqiZ6ZwZbQMzWGfQ6C3AX+=ouH+=ng@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 7bit
Content-Language: en-US
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Jul 2021 03:07:05.1645
 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: 83cc6103-438c-4f3f-68df-08d953071c35
X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a
X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.112.34];Helo=[mail.nvidia.com]
X-MS-Exchange-CrossTenant-AuthSource: CO1NAM11FT012.eop-nam11.prod.protection.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Anonymous
X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL1PR12MB5320
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


On 6/27/21 4:49 AM, Linus Walleij wrote:
> On Sat, Jun 26, 2021 at 1:48 AM Dipen Patel <dipenp@nvidia.com> wrote:
>
> Just a quick question about this:
>
>> +        GPIO_V2_LINE_FLAG_EVENT_CLOCK_HARDWARE | \
> Is the usage intended to be such that since hardware timestamp
> can not be guaranteed we need to ask for it and fail and if that
> fails maybe the software wants to fall back to the realtime or
> common timestamp?
>
> I'm thinking from the view of libgpiod or similar apps that abstract
> this and they will be "I want to use hardware timestamps if and
> only if it is available, otherwise I want to use this other timestamp"
> or is that use case uncommon, such that either you know exactly
> what you want or you should not be messing with hardware
> timestamps?


The way currently is implemented, if you have requested

FLAG_EVENT_CLOCK_HARDWARE and it fails, control will return

to userspace with an error. There is no fallback.

>
> Yours,
> Linus Walleij