From mboxrd@z Thu Jan 1 00:00:00 1970 From: Brian Norris Subject: Re: [PATCH 1/2] mfd: cros ec: spi: Don't send first message too soon Date: Mon, 13 Nov 2017 13:19:23 -0800 Message-ID: <20171113211900.GA126873@google.com> References: <1510607140-30582-1-git-send-email-jonathanh@nvidia.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1510607140-30582-1-git-send-email-jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org> Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Jon Hunter Cc: Lee Jones , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Shawn Nematbakhsh , Benson Leung , Doug Anderson List-Id: linux-tegra@vger.kernel.org + others On Mon, Nov 13, 2017 at 09:05:39PM +0000, Jon Hunter wrote: > On the Tegra124 Nyan-Big chromebook the very first SPI message sent to > the EC is failing. > > The Tegra SPI driver configures the SPI chip-selects to be active-high > by default (and always has for many years). The EC SPI requires an > active-low chip-select and so the Tegra chip-select is reconfigured to > be active-low when the EC SPI driver calls spi_setup(). The problem is > that if the first SPI message to the EC is sent too soon after > reconfiguring the SPI chip-select, it fails. > > The EC SPI driver prevents back-to-back SPI messages being sent too > soon by keeping track of the time the last transfer was sent via the > variable 'last_transfer_ns'. To prevent the very first transfer being > sent too soon, initialise the 'last_transfer_ns' variable after calling > spi_setup() and before sending the first SPI message. > > Signed-off-by: Jon Hunter > --- > Looks like this issue has been around for several Linux releases now > and it just depends on timing if this issue is seen or not and so there > is no specific commit this fixes. However, would be good to include for > v4.15. I wonder if that doesn't mean we should have a stable tag still? Cc: > drivers/mfd/cros_ec_spi.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/drivers/mfd/cros_ec_spi.c b/drivers/mfd/cros_ec_spi.c > index c9714072e224..a14196e95e9b 100644 > --- a/drivers/mfd/cros_ec_spi.c > +++ b/drivers/mfd/cros_ec_spi.c > @@ -667,6 +667,7 @@ static int cros_ec_spi_probe(struct spi_device *spi) > sizeof(struct ec_response_get_protocol_info); > ec_dev->dout_size = sizeof(struct ec_host_request); > > + ec_spi->last_transfer_ns = ktime_get_ns(); Seems pretty reasonable to me: Reviewed-by: Brian Norris > > err = cros_ec_register(ec_dev); > if (err) { > -- > 2.7.4 >