linux-kernel - Re: [PATCH] serial: 8250_bcm7271: improve bcm7271 8250 port

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Message-ID: <533b62f7-a6c2-b360-13e0-b873a1a54251@broadcom.com>
Date:   Mon, 14 Aug 2023 09:28:02 -0700
From:   Justin Chen <justin.chen@...adcom.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-serial@...r.kernel.org, opendmb@...il.com,
        Al Cooper <alcooperx@...il.com>,
        Broadcom internal kernel review list 
        <bcm-kernel-feedback-list@...adcom.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        John Ogness <john.ogness@...utronix.de>,
        Jiaqing Zhao <jiaqing.zhao@...ux.intel.com>,
        "open list:TTY LAYER" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] serial: 8250_bcm7271: improve bcm7271 8250 port



On 8/14/23 8:12 AM, Andy Shevchenko wrote:
> On Sat, Aug 12, 2023 at 09:24:21PM -0700, Justin Chen wrote:
>> On Sat, Aug 12, 2023 at 3:50 AM Greg Kroah-Hartman
>> <gregkh@...uxfoundation.org> wrote:
>>> On Fri, Aug 11, 2023 at 03:14:01PM -0700, Justin Chen wrote:
> 
>>>> +     [PORT_BCM7271] = {
>>>> +             .name           = "bcm7271_uart",
> 
> This is badly named port type.
> 

Would "Brcmstb 7271 UART" suffice?

>>>> +             .fifo_size      = 32,
>>>> +             .tx_loadsz      = 32,
>>>> +             .fcr            = UART_FCR_ENABLE_FIFO | UART_FCR_R_TRIG_01,
>>>> +             .rxtrig_bytes   = {1, 8, 16, 30},
>>>> +             .flags          = UART_CAP_FIFO | UART_CAP_AFE
>>>> +     },
>>>>   };
> 
> This is almost a dup of PORT_ALTR_16550_F32. Use it if you wish.
> You can always rename it if it feels the right thing to do.
> 

There is some other PORT_ALTR logic that I would like to avoid. I would 
also like to avoid future changes to PORT_ALTR that wouldn't be 
applicable to us.

> But why 8 and not 16 is the default rxtrig?
> 

We were seeing some latency issues on our chips where 16 would cause 
overflows. Trying to kill 2 birds with one stone. If creating another 
port type is avoidable then alternatively I can change the default in 
userspace.

Thanks,
Justin

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