From: Jiri Slaby <jirislaby@kernel.org>
To: Cristian Ciocaltea <cristian.ciocaltea@gmail.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Andreas Färber" <afaerber@suse.de>,
"Manivannan Sadhasivam" <manivannan.sadhasivam@linaro.org>,
linux-serial@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-actions@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/1] tty: serial: owl: Add support for kernel debugger
Date: Fri, 8 Jan 2021 08:58:38 +0100 [thread overview]
Message-ID: <02c664f5-8107-7757-2e20-c446a0458539@kernel.org> (raw)
In-Reply-To: <20210107181604.GA427955@BV030612LT>
On 07. 01. 21, 19:16, Cristian Ciocaltea wrote:
> Hi Greg,
>
> Thank you for the review!
>
> On Thu, Jan 07, 2021 at 04:20:55PM +0100, Greg Kroah-Hartman wrote:
>> On Tue, Jan 05, 2021 at 07:02:02PM +0200, Cristian Ciocaltea wrote:
>>> Implement 'poll_put_char' and 'poll_get_char' callbacks in struct
>>> 'owl_uart_ops' that enables OWL UART to be used for kernel debugging
>>> over serial line.
>>>
>>> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@gmail.com>
>
> [...]
>
>>> +
>>> +static void owl_uart_poll_put_char(struct uart_port *port, unsigned char ch)
>>> +{
>>> + while (owl_uart_read(port, OWL_UART_STAT) & OWL_UART_STAT_TFFU)
>>> + cpu_relax();
>>
>> Unbounded loops? What could possibly go wrong?
>>
>> :(
>>
>> Please don't do that in the kernel, put a max bound on this.
>
> I didn't realize the issue since I had encountered this pattern in many
> other serial drivers, as well: altera_uart, arc_uart, atmel_serial, etc.
>
>> And are you _SURE_ that cpu_relax() is what you want to call here?
>
> I'm thinking of replacing the loop with 'readl_poll_timeout_atomic()',
> if that would be a better approach.
It might be better, yes. Either way, if you add a bound to the loop, you
definitely need a more precise timing, so ndelay/udelay instead of
cpu_relax.
thanks,
--
js
next prev parent reply other threads:[~2021-01-08 7:59 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-05 17:02 [PATCH v2 1/1] tty: serial: owl: Add support for kernel debugger Cristian Ciocaltea
2021-01-07 15:20 ` Greg Kroah-Hartman
2021-01-07 18:16 ` Cristian Ciocaltea
2021-01-08 7:58 ` Jiri Slaby [this message]
2021-01-08 14:10 ` Cristian Ciocaltea
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