Hi Nishanth
My comments below.
Regards
Deepak
-----Original Message-----
From: Menon, Nishanth
Sent: Friday, April 09, 2010 12:00 PM
To: linux-omap
Cc: Kattungal, Deepak; Raja, Govindraj; Kevin Hilman; Tero Kristo
Subject: Re: [PM][PATCH 2/4] OMAP3: Serial: Errata i202: fix for MDR1 access
Menon, Nishanth had written, on 04/08/2010 12:54 PM, the following:
> From: Deepak K <deepak.k@xxxxxx>
[...]
>
> Cc: Govindraj R <govindraj.raja@xxxxxx>
> Cc: Kevin Hilman <khilman@xxxxxxxxxxxxxxxxxxx>
> Cc: Tero Kristo <tero.kristo@xxxxxxxxx>
>
> Signed-off-by: Deepak K <deepak.k@xxxxxx>
> Signed-off-by: Nishanth Menon <nm@xxxxxx>
> ---
> Note: original patch was done for android kernel, ported and sanity
> tested
>
> arch/arm/mach-omap2/serial.c | 18 +++++++++++++++++-
> 1 files changed, 17 insertions(+), 1 deletions(-)
>
> diff --git a/arch/arm/mach-omap2/serial.c b/arch/arm/mach-omap2/serial.c
> index 86d3b47..144033f 100644
> --- a/arch/arm/mach-omap2/serial.c
> +++ b/arch/arm/mach-omap2/serial.c
> @@ -223,6 +223,19 @@ static void omap_uart_restore_context(struct omap_uart_state *uart)
> uart->context_valid = 0;
>
> serial_write_reg(p, UART_OMAP_MDR1, 0x7);
> + /*
> + * Work Around for Errata i202 (3430 - 1.12, 3630 - 1.6)
> + * The access to uart register after MDR1 Access
> + * causes UART to corrupt data.
> + *
> + * Need a delay =
> + * 5 L4 clock cycles + 5 UART functional clock cycle (@48MHz = ~0.2uS)
> + * give 10 times as much
> + */
> + udelay(2);
> + /* TX and RX FIFO Clear; FIFO dis */
> + serial_write_reg(p, UART_FCR, 0xA6);
NAK
Late realization: should be checking if FIFO clear actually occurred
before proceeding (FIFO clear bits will be cleared by h/w once it is
complete,
so need to add a
/* wait till TX and RX fifos are cleard by h/w */
while(serial_read_reg(p, UART_FCR) & 0x06)
;
Deepak : The FCR is a Write-Only Register, the read to it wont return the correct value. If at all we need to add a check, the LSR should be read for the status of the FIFO. The same follows for the below section also.
> +
> serial_write_reg(p, UART_LCR, 0xBF); /* Config B mode */
> efr = serial_read_reg(p, UART_EFR);
> serial_write_reg(p, UART_EFR, UART_EFR_ECB);
> @@ -235,7 +248,6 @@ static void omap_uart_restore_context(struct omap_uart_state *uart)
> serial_write_reg(p, UART_IER, uart->ier);
> serial_write_reg(p, UART_LCR, 0x80);
> serial_write_reg(p, UART_MCR, uart->mcr);
> - serial_write_reg(p, UART_FCR, 0xA1);
> serial_write_reg(p, UART_LCR, 0xBF); /* Config B mode */
> serial_write_reg(p, UART_EFR, efr);
> serial_write_reg(p, UART_LCR, UART_LCR_WLEN8);
> @@ -243,6 +255,10 @@ static void omap_uart_restore_context(struct omap_uart_state *uart)
> serial_write_reg(p, UART_OMAP_WER, uart->wer);
> serial_write_reg(p, UART_OMAP_SYSC, uart->sysc);
> serial_write_reg(p, UART_OMAP_MDR1, 0x00); /* UART 16x mode */
> + /* Errata: i202 */
> + udelay(2);
> + /* TX and RX FIFO Clear; FIFO en */
> + serial_write_reg(p, UART_FCR, 0xA7);
NAK
same reason
> }
> #else
> static inline void omap_uart_save_context(struct omap_uart_state *uart) {}
I will post a v2 patch in a few mins..
--
Regards,
Nishanth Menon
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