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charset="us-ascii" Content-Transfer-Encoding: quoted-printable DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1566898175; bh=WLOz2gFlQelo20KM8Qz7RIw9KX7/ORHYu+5eJbF9HkE=; h=X-PGP-Universal:ARC-Seal:ARC-Message-Signature: ARC-Authentication-Results:From:To:CC:Subject:Thread-Topic: Thread-Index:Date:Message-ID:References:In-Reply-To: Accept-Language:X-MS-Has-Attach:X-MS-TNEF-Correlator:msip_labels: authentication-results:x-originating-ip:x-ms-publictraffictype: x-ms-office365-filtering-correlation-id:x-microsoft-antispam: x-ms-traffictypediagnostic:x-ms-exchange-transport-forked: x-microsoft-antispam-prvs:x-ms-oob-tlc-oobclassifiers: x-forefront-prvs:x-forefront-antispam-report:received-spf: x-ms-exchange-senderadcheck:x-microsoft-antispam-message-info: MIME-Version:X-MS-Exchange-CrossTenant-Network-Message-Id: X-MS-Exchange-CrossTenant-originalarrivaltime: X-MS-Exchange-CrossTenant-fromentityheader: X-MS-Exchange-CrossTenant-id:X-MS-Exchange-CrossTenant-mailboxtype: X-MS-Exchange-CrossTenant-userprincipalname: X-MS-Exchange-Transport-CrossTenantHeadersStamped:X-OriginatorOrg: Content-Language:Content-Type:Content-Transfer-Encoding; b=Q1UgZvdmIu3Q3PfAgLW7nIbFgDiLIur+5y68V+pEm9A+dHQ3qu/CFaXuY1mJXI8JZ wgWf4k+Z11M3K8BXWf9QliP91HIcbpiyiiMxAkw1Z8FcKxQckuBCL+PkKuuuqjHcUs X6RbbTEAYoTZd732AVOWEUTZSqBdKaFGsrl6mUlf7Uk5u+sSDk/QIu+fiA3l5gl5z+ na5lTCcbx1+8fhGB2V8rN2K9F06qUOlNZtCo/I5ZEtMjywUKT362wAfXU/2Q6W5Pvw OQpjSk4PkKRxNZhBJBtUoP0Z4XBE+TrUOGiY1P0vMjnZKG0RfkkYPHkIff2xsPXLIk S/mAvB6JI4Npw== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > -----Original Message----- > From: linux-tegra-owner@vger.kernel.org owner@vger.kernel.org> On Behalf Of Thierry Reding > Sent: Tuesday, August 13, 2019 3:16 PM > To: Krishna Yarlagadda > Cc: gregkh@linuxfoundation.org; robh+dt@kernel.org;=20 > mark.rutland@arm.com; Jonathan Hunter ; Laxman=20 > Dewangan ; jslaby@suse.com; linux-=20 > serial@vger.kernel.org; devicetree@vger.kernel.org; linux-=20 > tegra@vger.kernel.org; linux-kernel@vger.kernel.org; Ahung Cheng=20 > ; Shardar Mohammed > Subject: Re: [PATCH 03/14] serial: tegra: avoid reg access when clk=20 > disabled >=20 > On Mon, Aug 12, 2019 at 04:58:12PM +0530, Krishna Yarlagadda wrote: > > From: Ahung Cheng > > > > This avoids two race conditions from the UART shutdown sequence both=20 > > leading to 'Machine check error in AXI2APB' and kernel oops. > > > > One was that the clock was disabled before the DMA was terminated=20 > > making it possible for the DMA callbacks to be called after the=20 > > clock was disabled. These callbacks could write to the UART=20 > > registers causing timeout. > > > > The second was that the clock was disabled before the UART was=20 > > completely flagged as closed. This is done after the shutdown is=20 > > called and a new write could be started after the clock was disabled. > > tegra_uart_start_pio_tx could be called causing timeout. > > > > Given that the baud rate is reset at the end of shutdown sequence,=20 > > this fix is to examine the baud rate to avoid register access from=20 > > both race conditions. > > > > Besides, terminate the DMA before disabling the clock. > > > > Signed-off-by: Ahung Cheng > > Signed-off-by: Shardar Mohammed > > Signed-off-by: Krishna Yarlagadda > > --- > > drivers/tty/serial/serial-tegra.c | 17 +++++++++++------ > > 1 file changed, 11 insertions(+), 6 deletions(-) > > > > diff --git a/drivers/tty/serial/serial-tegra.c > > b/drivers/tty/serial/serial-tegra.c > > index 93d299e..d908465 100644 > > --- a/drivers/tty/serial/serial-tegra.c > > +++ b/drivers/tty/serial/serial-tegra.c > > @@ -126,6 +126,8 @@ struct tegra_uart_port { > > > > static void tegra_uart_start_next_tx(struct tegra_uart_port *tup);=20 > > static int tegra_uart_start_rx_dma(struct tegra_uart_port *tup); > > +static void tegra_uart_dma_channel_free(struct tegra_uart_port *tup, > > + bool dma_to_memory); > > > > static inline unsigned long tegra_uart_read(struct tegra_uart_port *tu= p, > > unsigned long reg) > > @@ -458,6 +460,9 @@ static void tegra_uart_start_next_tx(struct > tegra_uart_port *tup) > > unsigned long count; > > struct circ_buf *xmit =3D &tup->uport.state->xmit; > > > > + if (WARN_ON(!tup->current_baud)) > > + return; >=20 > Are the race conditions that you are describing something which can be=20 > triggered by the user? If so, it's not a good idea to use a WARN_ON,=20 > because that could lead to some userspace spamming the log with these,=20 > potentially on purpose. >=20 > Thierry >=20 These are triggered by user events. I will remove WARN_ON KY > > + > > tail =3D (unsigned long)&xmit->buf[xmit->tail]; > > count =3D CIRC_CNT_TO_END(xmit->head, xmit->tail, > UART_XMIT_SIZE); > > if (!count) > > @@ -829,6 +834,12 @@ static void tegra_uart_hw_deinit(struct > tegra_uart_port *tup) > > tup->current_baud =3D 0; > > spin_unlock_irqrestore(&tup->uport.lock, flags); > > > > + tup->rx_in_progress =3D 0; > > + tup->tx_in_progress =3D 0; > > + > > + tegra_uart_dma_channel_free(tup, true); > > + tegra_uart_dma_channel_free(tup, false); > > + > > clk_disable_unprepare(tup->uart_clk); > > } > > > > @@ -1066,12 +1077,6 @@ static void tegra_uart_shutdown(struct > uart_port *u) > > struct tegra_uart_port *tup =3D to_tegra_uport(u); > > > > tegra_uart_hw_deinit(tup); > > - > > - tup->rx_in_progress =3D 0; > > - tup->tx_in_progress =3D 0; > > - > > - tegra_uart_dma_channel_free(tup, true); > > - tegra_uart_dma_channel_free(tup, false); > > free_irq(u->irq, tup); > > } > > > > -- > > 2.7.4 > >