[RFC] mtd: Fix error code loss in mtdchar_read() function.

[Richard Weinberger]

----- Ursprüngliche Mail -----
> Von: "ZhaoLong Wang" <wangzhaolong1 at huawei.com>
> An: "Miquel Raynal" <miquel.raynal at bootlin.com>, "richard" <richard at nod.at>, "Vignesh Raghavendra" <vigneshr at ti.com>
> CC: "linux-mtd" <linux-mtd at lists.infradead.org>, "linux-kernel" <linux-kernel at vger.kernel.org>, "chengzhihao1"
> <chengzhihao1 at huawei.com>, "ZhaoLong Wang" <wangzhaolong1 at huawei.com>, "yi zhang" <yi.zhang at huawei.com>, "yangerkun"
> <yangerkun at huawei.com>
> Gesendet: Samstag, 23. September 2023 02:58:56
> Betreff: [RFC] mtd: Fix error code loss in mtdchar_read() function.

> In the first while loop, if the mtd_read() function returns -EBADMSG
> and 'retlen' returns 0, the loop break and the function returns value
> 'total_retlen' is 0, not the error code.

Given this a second thought. I don't think a NAND driver is allowed to return
less than requests bytes and setting EBADMSG.
UBI's IO path has a comment on that:

                /*
                 * The driver should never return -EBADMSG if it failed to read
                 * all the requested data. But some buggy drivers might do
                 * this, so we change it to -EIO.
                 */
                if (read != len && mtd_is_eccerr(err)) {
                        ubi_assert(0);
                        err = -EIO;
                }

Thanks,
//richard