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;
Subject: Re: [PATCH v5 15/15] misc: bcm-vk: add ttyVK support
To:     Florian Fainelli <f.fainelli@gmail.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Olof Johansson <olof@lixom.net>
Cc:     Kees Cook <keescook@chromium.org>, linux-kernel@vger.kernel.org,
        bcm-kernel-feedback-list@broadcom.com
References: <20201001012810.4172-1-scott.branden@broadcom.com>
 <20201001012810.4172-16-scott.branden@broadcom.com>
 <278afb05-8c8d-98d2-eed0-f73b954b03c7@gmail.com>
From:   Scott Branden <scott.branden@broadcom.com>
Message-ID: <140a5cde-67fd-f4b1-e4a9-9c68adf964c4@broadcom.com>
Date:   Thu, 1 Oct 2020 15:26:41 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.10.0
MIME-Version: 1.0
In-Reply-To: <278afb05-8c8d-98d2-eed0-f73b954b03c7@gmail.com>
Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-256;
        boundary="000000000000dc278a05b0a38256"
Precedence: bulk

--000000000000dc278a05b0a38256
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8bit
Content-Language: en-CA

Hi Florian,

On 2020-09-30 7:36 p.m., Florian Fainelli wrote:
>
>
> On 9/30/2020 6:28 PM, Scott Branden wrote:
>> Add ttyVK support to driver to allow console access to VK card from host.
>>
>> Device node will be in the follow form /dev/bcm-vk.x_ttyVKy where:
>> x is the instance of the VK card
>> y is the tty device number on the VK card
>>
>> Signed-off-by: Scott Branden <scott.branden@broadcom.com>
>
> Was it not possible to:
>
> - emulate a standard 8250 UART and just expose an additional bar + MSI vector such that one could get a debug UART out of this device with little to no work on the host side?
I don't see how such emulation is simpler than what we have.  For a standard 8250 UART implementation how would we emulate a FIFO in memory accessible over PCIe.  I don't see how to do that with shared memory?  Also, we don't have an additional bar available on the PCIe device.  There is currently little to no work on the device side using a circular buffer with read and write pointers.
>
> - or use virtio console and implement virtio on the firmware that runs on VK?
Not that possible as the debug/console UARTs are used inside and outside of linux on the VK card.
>
> It's not a lot of code, but it just feels like this should not have to be done at all.
If there was a simpler way to do it, yes, I would like a "UART" running over PCIe shared memory via a circular buffer.
And that is what the code we developed does.


--000000000000dc278a05b0a38256
Content-Type: application/pkcs7-signature; name="smime.p7s"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="smime.p7s"
Content-Description: S/MIME Cryptographic Signature
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--000000000000dc278a05b0a38256--