linux-kernel - Re: [PATCH v3 1/5] w1: ds2490: support block sizes larger than 128 bytes in ds_read

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Message-ID: <5ccc0a13-01e1-464c-980b-bdf34970cc33@kernel.org>
Date:   Sat, 2 Dec 2023 13:01:42 +0100
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     marc.ferland@...il.com, krzysztof.kozlowski@...aro.org
Cc:     gregkh@...uxfoundation.org, marc.ferland@...atest.com,
        jeff.dagenais@...il.com, rdunlap@...radead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/5] w1: ds2490: support block sizes larger than 128
 bytes in ds_read_block

On 30/11/2023 14:52, marc.ferland@...il.com wrote:
> From: Marc Ferland <marc.ferland@...atest.com>
> 
> The current ds_read_block function only supports block sizes up to
> 128 bytes, which is the depth of the 'data out' fifo on the ds2490.
> 
> Reading larger blocks will fail with a: -110 (ETIMEDOUT) from
> usb_control_msg(). Example:
> 
>     $ dd if=/sys/bus/w1/devices/43-000000478756/eeprom bs=256 count=1
> 
> yields to the following message from the kernel:
> 
>     usb 5-1: Failed to write 1-wire data to ep0x2: err=-110.
> 
> I discovered this issue while implementing support for the ds28ec20
> eeprom in the w1-2433 driver. This driver accepts reading blocks of
> sizes up to the size of the entire memory (2560 bytes in the case of
> the ds28ec20). Note that this issue _does not_ arises when the kernel
> is configured with CONFIG_W1_SLAVE_DS2433_CRC enabled since in this
> mode the driver reads one 32 byte block at a time (a single memory
> page).
> 
> Also, from the ds2490 datasheet (2995.pdf, page 22, BLOCK I/O
> command):
> 
>      For a block write sequence the EP2 FIFO must be pre-filled with
>      data before command execution. Additionally, for block sizes
>      greater then the FIFO size, the FIFO content status must be
>      monitored by host SW so that additional data can be sent to the
>      FIFO when necessary. A similar EP3 FIFO content monitoring
>      requirement exists for block read sequences. During a block read
>      the number of bytes loaded into the EP3 FIFO must be monitored so
>      that the data can be read before the FIFO overflows.
> 
> Breaking the buffer in 128 bytes blocks and simply calling the
> original code sequence has solved the issue for me.
> 
> Tested with a DS1490F usb<->one-wire adapter and both the DS28EC20 and
> DS2433 eeprom memories.
> 
> Note: The v1 of this patch changed both the ds_read_block and
> ds_write_block functions, but since I don't have any way to test the
> 'write' part with writes bigger than a page size (maximum accepted by
> my eeprom), I preferred not to make any assumptions and I just
> removed that part.

Drop that paragraph, not really helping to understand the commit once
accepted.

> 
> Signed-off-by: Marc Ferland <marc.ferland@...atest.com>
> ---
>  drivers/w1/masters/ds2490.c | 25 +++++++++++++++++++++----
>  1 file changed, 21 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/w1/masters/ds2490.c b/drivers/w1/masters/ds2490.c
> index 5f5b97e24700..b6e244992c15 100644
> --- a/drivers/w1/masters/ds2490.c
> +++ b/drivers/w1/masters/ds2490.c
> @@ -98,6 +98,8 @@
>  #define ST_EPOF				0x80
>  /* Status transfer size, 16 bytes status, 16 byte result flags */
>  #define ST_SIZE				0x20
> +/* 1-wire data i/o fifo size, 128 bytes */
> +#define FIFO_SIZE			0x80
>  
>  /* Result Register flags */
>  #define RR_DETECT			0xA5 /* New device detected */
> @@ -614,14 +616,11 @@ static int ds_read_byte(struct ds_device *dev, u8 *byte)
>  	return 0;
>  }
>  
> -static int ds_read_block(struct ds_device *dev, u8 *buf, int len)
> +static int __read_block(struct ds_device *dev, u8 *buf, int len)

Drop __ and name the function descriptive. It's confusing to have two
times read_block(). Just name them according to what they really do.

Best regards,
Krzysztof