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
WARNING: multiple messages have this Message-ID (diff)
From: Cristian Ciocaltea <cristian.ciocaltea@gmail.com> To: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: linux-actions@lists.infradead.org, linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, "Manivannan Sadhasivam" <manivannan.sadhasivam@linaro.org>, "Jiri Slaby" <jirislaby@kernel.org>, "Andreas Färber" <afaerber@suse.de>, linux-arm-kernel@lists.infradead.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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2021-01-07 18:17 UTC|newest] Thread overview: 10+ 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 2021-01-05 17:02 ` Cristian Ciocaltea 2021-01-07 15:20 ` Greg Kroah-Hartman 2021-01-07 15:20 ` Greg Kroah-Hartman 2021-01-07 18:16 ` Cristian Ciocaltea [this message] 2021-01-07 18:16 ` Cristian Ciocaltea 2021-01-08 7:58 ` Jiri Slaby 2021-01-08 7:58 ` Jiri Slaby 2021-01-08 14:10 ` Cristian Ciocaltea 2021-01-08 14:10 ` Cristian Ciocaltea
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