On Tue, Jun 8, 2021 at 5:40 PM Luben Tuikov <luben.tuikov@xxxxxxx> wrote:
>
> * When reading from the EEPROM device, there is no
> device limitation on the number of bytes
> read--they're simply sequenced out. Thus, read
> the whole data requested in one go.
>
> * When writing to the EEPROM device, there is a
> 256-byte page limit to write to before having to
> generate a STOP on the bus, as well as the
> address written to mustn't cross over the page
> boundary (it actually rolls over). Maximize the
> data written to per bus acquisition.
>
> * Return the number of bytes read/written, or -errno.
>
> * Add kernel doc.
>
> Cc: Jean Delvare <jdelvare@xxxxxxx>
> Cc: Alexander Deucher <Alexander.Deucher@xxxxxxx>
> Cc: Andrey Grodzovsky <Andrey.Grodzovsky@xxxxxxx>
> Cc: Lijo Lazar <Lijo.Lazar@xxxxxxx>
> Cc: Stanley Yang <Stanley.Yang@xxxxxxx>
> Cc: Hawking Zhang <Hawking.Zhang@xxxxxxx>
> Signed-off-by: Luben Tuikov <luben.tuikov@xxxxxxx>
Acked-by: Alex Deucher <alexander.deucher@xxxxxxx>
> ---
> drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.c | 96 +++++++++++++++-------
> 1 file changed, 68 insertions(+), 28 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.c
> index d02ea083a6c69b..7fdb5bd2fc8bc8 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.c
> @@ -24,59 +24,99 @@
> #include "amdgpu_eeprom.h"
> #include "amdgpu.h"
>
> -#define EEPROM_OFFSET_LENGTH 2
> +/* AT24CM02 has a 256-byte write page size.
> + */
> +#define EEPROM_PAGE_BITS 8
> +#define EEPROM_PAGE_SIZE (1U << EEPROM_PAGE_BITS)
> +#define EEPROM_PAGE_MASK (EEPROM_PAGE_SIZE - 1)
> +
> +#define EEPROM_OFFSET_SIZE 2
>
> +/**
> + * amdgpu_eeprom_xfer -- Read/write from/to an I2C EEPROM device
> + * @i2c_adap: pointer to the I2C adapter to use
> + * @slave_addr: I2C address of the slave device
> + * @eeprom_addr: EEPROM address from which to read/write
> + * @eeprom_buf: pointer to data buffer to read into/write from
> + * @buf_size: the size of @eeprom_buf
> + * @read: True if reading from the EEPROM, false if writing
> + *
> + * Returns the number of bytes read/written; -errno on error.
> + */
> int amdgpu_eeprom_xfer(struct i2c_adapter *i2c_adap,
> u16 slave_addr, u16 eeprom_addr,
> - u8 *eeprom_buf, u16 bytes, bool read)
> + u8 *eeprom_buf, u16 buf_size, bool read)
> {
> - u8 eeprom_offset_buf[2];
> - u16 bytes_transferred;
> + u8 eeprom_offset_buf[EEPROM_OFFSET_SIZE];
> struct i2c_msg msgs[] = {
> {
> .addr = slave_addr,
> .flags = 0,
> - .len = EEPROM_OFFSET_LENGTH,
> + .len = EEPROM_OFFSET_SIZE,
> .buf = eeprom_offset_buf,
> },
> {
> .addr = slave_addr,
> .flags = read ? I2C_M_RD : 0,
> - .len = bytes,
> - .buf = eeprom_buf,
> },
> };
> + const u8 *p = eeprom_buf;
> int r;
> + u16 len;
> +
> + r = 0;
> + for (len = 0; buf_size > 0;
> + buf_size -= len, eeprom_addr += len, eeprom_buf += len) {
> + /* Set the EEPROM address we want to write to/read from.
> + */
> + msgs[0].buf[0] = (eeprom_addr >> 8) & 0xff;
> + msgs[0].buf[1] = eeprom_addr & 0xff;
>
> - msgs[0].buf[0] = ((eeprom_addr >> 8) & 0xff);
> - msgs[0].buf[1] = (eeprom_addr & 0xff);
> + if (!read) {
> + /* Write the maximum amount of data, without
> + * crossing the device's page boundary, as per
> + * its spec. Partial page writes are allowed,
> + * starting at any location within the page,
> + * so long as the page boundary isn't crossed
> + * over (actually the page pointer rolls
> + * over).
> + *
> + * As per the AT24CM02 EEPROM spec, after
> + * writing into a page, the I2C driver MUST
> + * terminate the transfer, i.e. in
> + * "i2c_transfer()" below, with a STOP
> + * condition, so that the self-timed write
> + * cycle begins. This is implied for the
> + * "i2c_transfer()" abstraction.
> + */
> + len = min(EEPROM_PAGE_SIZE - (eeprom_addr &
> + EEPROM_PAGE_MASK),
> + (u32)buf_size);
> + } else {
> + /* Reading from the EEPROM has no limitation
> + * on the number of bytes read from the EEPROM
> + * device--they are simply sequenced out.
> + */
> + len = buf_size;
> + }
> + msgs[1].len = len;
> + msgs[1].buf = eeprom_buf;
>
> - while (msgs[1].len) {
> r = i2c_transfer(i2c_adap, msgs, ARRAY_SIZE(msgs));
> - if (r <= 0)
> - return r;
> + if (r < ARRAY_SIZE(msgs))
> + break;
>
> - /* Only for write data */
> - if (!msgs[1].flags)
> - /*
> - * According to EEPROM spec there is a MAX of 10 ms required for
> - * EEPROM to flush internal RX buffer after STOP was issued at the
> - * end of write transaction. During this time the EEPROM will not be
> - * responsive to any more commands - so wait a bit more.
> + if (!read) {
> + /* According to the AT24CM02 EEPROM spec the
> + * length of the self-writing cycle, tWR, is
> + * 10 ms.
> *
> * TODO Improve to wait for first ACK for slave address after
> * internal write cycle done.
> */
> msleep(10);
> -
> -
> - bytes_transferred = r - EEPROM_OFFSET_LENGTH;
> - eeprom_addr += bytes_transferred;
> - msgs[0].buf[0] = ((eeprom_addr >> 8) & 0xff);
> - msgs[0].buf[1] = (eeprom_addr & 0xff);
> - msgs[1].buf += bytes_transferred;
> - msgs[1].len -= bytes_transferred;
> + }
> }
>
> - return 0;
> + return r < 0 ? r : eeprom_buf - p;
> }
> --
> 2.32.0
>
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