From: Cristian Ciocaltea <cristian.ciocaltea@gmail.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Jiri Slaby" <jirislaby@kernel.org>,
"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: Thu, 7 Jan 2021 20:16:04 +0200 [thread overview]
Message-ID: <20210107181604.GA427955@BV030612LT> (raw)
In-Reply-To: <X/cm1+wVQpoXj5Xr@kroah.com>
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.
Kind regards,
Cristi
> thanks,
>
> greg k-h
next prev parent reply other threads:[~2021-01-07 18:17 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 [this message]
2021-01-08 7:58 ` Jiri Slaby
2021-01-08 14:10 ` Cristian Ciocaltea
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