RE: [PATCH net-next v3 3/9] ravb: Add aligned_tx to struct ravb_hw_info

Hi Geert,

Thanks for the feedback

Subject: Re: [PATCH net-next v3 3/9] ravb: Add aligned_tx to struct
ravb_hw_info

Hi Biju,

On Wed, Aug 18, 2021 at 9:08 PM Biju Das [off-list ref]
wrote:

quoted

R-Car Gen2 needs a 4byte aligned address for the transmission buffer,
whereas R-Car Gen3 doesn't have any such restriction.

Add aligned_tx to struct ravb_hw_info to select the driver to choose
between aligned and unaligned tx buffers.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>

Thanks for your patch, which is now commit 68ca3c923213b908 ("ravb:
Add aligned_tx to struct ravb_hw_info") in net-next.

quoted

--- a/drivers/net/ethernet/renesas/ravb.h
+++ b/drivers/net/ethernet/renesas/ravb.h

@@ -990,6 +990,7 @@ enum ravb_chip_id {

 struct ravb_hw_info {
        enum ravb_chip_id chip_id;
+       unsigned aligned_tx: 1;
 };

 struct ravb_private {

diff --git a/drivers/net/ethernet/renesas/ravb_main.c

b/drivers/net/ethernet/renesas/ravb_main.c
index b6554e5e13af..dbccf2cd89b2 100644

--- a/drivers/net/ethernet/renesas/ravb_main.c
+++ b/drivers/net/ethernet/renesas/ravb_main.c

@@ -1930,6 +1930,7 @@ static const struct ravb_hw_info

ravb_gen3_hw_info = {

 static const struct ravb_hw_info ravb_gen2_hw_info = {
        .chip_id = RCAR_GEN2,
+       .aligned_tx = 1,
 };

 static const struct of_device_id ravb_match_table[] = { @@ -2140,7
+2141,7 @@ static int ravb_probe(struct platform_device *pdev)
        ndev->max_mtu = 2048 - (ETH_HLEN + VLAN_HLEN + ETH_FCS_LEN);
        ndev->min_mtu = ETH_MIN_MTU;

-       priv->num_tx_desc = info->chip_id == RCAR_GEN2 ?
+       priv->num_tx_desc = info->aligned_tx ?
                NUM_TX_DESC_GEN2 : NUM_TX_DESC_GEN3;

At first look, this change does not seem to match the patch description.
Upon a deeper look, it is correct, as num_tx_desc is also used to control
alignment.

This changes introduced by the commit [1], where it used num_tx_desc related to 4byte alignment restriction.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/net/ethernet/renesas/ravb_main.c?h=v5.14-rc7&id=f543305da9b5a5efaf6fa61606e8bbc8977f406d

But now NUM_TX_DESC_GEN[23] no longer match their use.
Perhaps they should be renamed, or replaced by hardcoded values, with a
comment?

OK, will replace this macros with hardcoded values with a comment.

Regards,
Biju

    /*
     * FIXME: Explain the relationship between alignment and number of
buffers
     */
    priv->num_tx_desc = info->aligned_tx ? 2 : 1;

quoted

        /* Set function */

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-
m68k.org

In personal conversations with technical people, I call myself a hacker.
But when I'm talking to journalists I just say "programmer" or something
like that.
                                -- Linus Torvalds