linux-kernel - Re: [PATCH AUTOSEL 5.13 013/114] serial: 8250: of: Check for CONFIG_SERIAL_8250

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Message-ID: <YPN4KiU/50HGeXHj@sashalap>
Date:   Sat, 17 Jul 2021 20:39:06 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Jim Quinlan <jim2101024@...il.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Al Cooper <alcooperx@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-serial@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 5.13 013/114] serial: 8250: of: Check for
 CONFIG_SERIAL_8250_BCM7271

On Fri, Jul 09, 2021 at 07:33:25PM -0700, Florian Fainelli wrote:
>
>
>On 7/9/2021 7:16 PM, Sasha Levin wrote:
>>From: Jim Quinlan <jim2101024@...il.com>
>>
>>[ Upstream commit f5b08386dee439c7a9e60ce0a4a4a705f3a60dff ]
>>
>>Our SoC's have always had a NS16650A UART core and older SoC's would
>>have a compatible string of: 'compatible = ""ns16550a"' and use the
>>8250_of driver. Our newer SoC's have added enhancements to the base
>>core to add support for DMA and accurate high speed baud rates and use
>>this newer 8250_bcm7271 driver. The Device Tree node for our enhanced
>>UARTs has a compatible string of: 'compatible = "brcm,bcm7271-uart",
>>"ns16550a"''. With both drivers running and the link order setup so
>>that the 8250_bcm7217 driver is initialized before the 8250_of driver,
>>we should bind the 8250_bcm7271 driver to the enhanced UART, or for
>>upstream kernels that don't have the 8250_bcm7271 driver, we bind to
>>the 8250_of driver.
>>
>>The problem is that when both the 8250_of and 8250_bcm7271 drivers
>>were running, occasionally the 8250_of driver would be bound to the
>>enhanced UART instead of the 8250_bcm7271 driver. This was happening
>>because we use SCMI based clocks which come up late in initialization
>>and cause probe DEFER's when the two drivers get their clocks.
>>
>>Occasionally the SCMI clock would become ready between the 8250_bcm7271
>>probe and the 8250_of probe and the 8250_of driver would be bound. To
>>fix this we decided to config only our 8250_bcm7271 driver and added
>>"ns16665a0" to the compatible string so the driver would work on our
>>older system.
>>
>>This commit has of_platform_serial_probe() check specifically for the
>>"brcm,bcm7271-uart" and whether its companion driver is enabled. If it
>>is the case, and the clock provider is not ready, we want to make sure
>>that when the 8250_bcm7271.c driver returns EPROBE_DEFER, we are not
>>getting the UART registered via 8250_of.c.
>>
>>Reviewed-by: Andy Shevchenko <andy.shevchenko@...il.com>
>>Signed-off-by: Jim Quinlan <jim2101024@...il.com>
>>Signed-off-by: Al Cooper <alcooperx@...il.com>
>>Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
>>Link: https://lore.kernel.org/r/20210423183206.3917725-1-f.fainelli@gmail.com
>>Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>>Signed-off-by: Sasha Levin <sashal@...nel.org>
>
>This commit is only relevant with 
>41a469482de257ea8db43cf74b6311bd055de030 ("serial: 8250: Add new 
>8250-core based Broadcom STB driver") which is included in v5.13 and 
>newer. You would want to drop that commit from the 5.12, 5.10 and 5.4 
>auto-selection.

I'll drop it from 5.12 and older, thanks!

-- 
Thanks,
Sasha